Stabilized alpha-galactosidase and uses thereof

ABSTRACT

Multimeric protein structures comprising at least two alpha-galactosidase monomers being covalently linked to one another via a linking moiety are disclosed herein, as well a process for preparing same, and methods of treating Fabry disease via administration of a multimeric protein structure. The disclosed multimeric protein structures exhibit an improved performance, in terms of enhanced activity and/or a longer lasting activity under both lysosomal conditions and in a serum environment.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/582,482 filed on Sep. 4, 2012, now U.S. Pat. No. 9,194,011, issued onNov. 24, 2015, which is a National Phase of PCT Patent Application No.PCT/IL2011/000209 having International filing date of Mar. 2, 2011,which claims the benefit of priority under 35 USC §119(e) of U.S.Provisional Patent Application Nos. 61/309,487 filed on Mar. 2, 2010,61/434,499 filed on Jan. 20, 2011 and 61/434,503 filed on Jan. 20, 2011,and which is also a Continuation-In-Part (OP) of PCT Patent ApplicationNo. PCT/IL2010/000956 having International filing date of Nov. 17, 2010.

PCT Patent Application No. PCT/IL2010/000956 claims the benefit ofpriority under 35 USC §119(e) of U.S. Provisional Patent Application No.61/261,787 filed on Nov. 17, 2009. The contents of the aboveapplications are all incorporated by reference as if fully set forthherein in their entirety.

SEQUENCE LISTING STATEMENT

The ASCII file, entitled 64176SequenceListing.txt, created on Nov. 10,2015, comprising 79,026 bytes, submitted concurrently with the filing ofthis application is incorporated herein by reference.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to novelmultimeric protein structures and, more particularly, but notexclusively, to multimeric protein structures of α-galactosidase and touses thereof in treating Fabry disease.

The lysosomal enzyme α-galactosidase-A (α-GAL or α-Gal A; EC 3.2.1.22)catalyzes the removal of galactose from oligosaccharides, glycoproteinsand glycolipids during the catabolism of macromolecules. Deficiencies inlysosomal enzymes lead to the accumulation of their substrates in thetissues, conditions known as lysosomal storage diseases. In humans, theabsence of functional α-galactosidase-A leads to the accumulation ofglycolipids containing terminal α-galactose residues (primarilyglobotriaosylceramide, which is also referred to as “ceramidetrihexoside”, “CTH” or “Gb₃”) in the tissues, leading to Fabry disease.Fabry disease is an X-linked recessive disorder, first described in1898, characterized by chronic pain, ocular opacities, liver and kidneyimpairment, skin lesions, vascular deterioration and/or cardiacdeficiencies. Recombinant human α-galactosidase-A has the ability torestore enzyme function in patients, and enzyme replacement therapy(ERT) using α-GAL was approved in the United States in 2003 as atreatment for Fabry disease. α-GAL became the second recombinant proteinapproved for the treatment of a lysosomal storage disorder afterβ-glucosidase, a treatment for Gaucher disease.

Endogenous and recombinant α-GALs catalyze the hydrolysis of terminalgalactosylated glycolipids in the lysosomes of cells of organs such asthe liver, kidneys, spleen, heart, etc. This natural action site ischaracterized by its low pH, reaching as low as 4.5. Lysosomal enzymes,including α-GAL, are hence designed to exert their maximal activity atthese low pH levels.

Current Fabry ERT treatments are based on mammalian-cell derivedrecombinant α-GAL which is considered to be a limited efficiencytreatment. These treatments only decelerate the progress of the diseasebut are not able to stop its progress and do not offer a true andcomplete solution. Furthermore, in some cases, ERT with commercialrecombinant α-GALs must be ceased due to development of an immunogenicresponse to the treatment and in some cases the treatment cannot beinitiated in light of immunogenicity problems.

X-ray structure analysis reveals that human α-GAL is a homodimericglycoprotein with each monomer composed of two domains, a (β/α)₈ domaincontaining the active site and a C-terminal domain containing eightantiparallel β strands on two sheets in a β sandwich [Garman & Garboczi,J Mol Biol 2004, 337:319-335]. The two monomers are arranged in ahead-to-tail assembly and the dimerization is non-covalent. The twomonomers pack with an interface that extends the 75 Å width of the dimerand buries 2200 Å² of surface area. In the dimer interface, 30 residuesfrom each monomer contribute to the interface. The two active sites ofthe dimer are separated by approximately 50 Å.

The crystal structure of α-Gal was solved for a non-liganded protein aswell as for a galactose-liganded protein. These two structures exhibitlittle change between the liganded and non-liganded structures.Nevertheless, the use of galactose instead of the natural substrate,globotriaosylceramide (Gb₃), the latter characterized by long lipidicchains able to interact with the hydrophobic domain of one monomer whilethe terminal galactose interacts with the active site of the secondmonomer, may not lead to evidence of active site cooperativity.Furthermore, biochemical evidence does suggest such cooperativity,exemplifying the importance of the homodimeric quaternary structure[Bishop & Desnick, J Biol Chem 1981, 256:1307-1316]. Thus, the kineticproperties of human α-Gal were studied and cooperativity between themonomers of the homodimeric enzyme, each with an interacting catalyticsite, was shown. It was therefore suggested that enzymatic activity andstability may be dependent on dimerization.

WO 2009/024977, by the present assignee, which is incorporated byreference as if fully set forth herein, teaches conjugates of asaccharide and a biomolecule, covalently linked therebetween via anon-hydrophobic linker, as well as medical uses utilizing suchconjugates.

PCT International Patent Application No. PCT/IL2010/000956, by thepresent assignee, teaches methodologies which utilize α-galactosidasewhich exhibits a lysosomal activity at pH levels higher than lysosomalpH.

Additional background art include Bendele et al. [Toxicological Sciences1998, 42:152-157], U.S. Pat. Nos. 5,256,804, 5,580,757 and 5,766,897,International Patent Application PCT/NL2007/050684 (published as WO2008/075957), and Seely & Richey [J Chromatography A 2001, 908:235-241].

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present inventionthere is provided a multimeric protein structure comprising at least twoα-galactosidase monomers being covalently linked to one another via alinking moiety, the multimeric protein structure featuring acharacteristic selected from the group consisting of:

(a) an α-galactosidase activity upon subjecting the multimeric proteinstructure to human plasma conditions for one hour, which is at least 10%higher than an activity of native α-galactosidase upon subjecting thenative α-galactosidase to human plasma conditions for one hour;

(b) an α-galactosidase activity which decreases upon subjecting themultimeric protein structure to human plasma conditions for one hour bya percentage which is at least 10% less than the percentage by which anactivity of the native α-galactosidase decreases upon subjecting thenative α-galactosidase to human plasma conditions for one hour;

(c) an α-galactosidase activity which remains substantially unchangedupon subjecting the multimeric protein structure to human plasmaconditions for one hour;

(d) an α-galactosidase activity, upon subjecting the multimeric proteinstructure to lysosomal conditions for one week, which is at least 10%higher than an activity of native α-galactosidase upon subjecting thenative α-galactosidase to lysosomal conditions for one week;

(e) an α-galactosidase activity which decreases upon subjecting themultimeric protein structure to lysosomal conditions for one day by apercentage which is at least 10% less than the percentage by which anactivity of the native α-galactosidase decreases upon subjecting thenative α-galactosidase to lysosomal conditions for one day;

(f) an α-galactosidase activity which remains substantially unchangedupon subjecting the multimeric protein structure to lysosomal conditionsfor one day;

(g) an α-galactosidase activity, immediately upon subjecting themultimeric protein structure to lysosomal conditions, which is at least10% higher than an activity of native α-galactosidase immediately uponsubjecting the native form of the protein to lysosomal conditions;

(h) an α-galactosidase activity, immediately upon subjecting themultimeric protein structure to an aqueous solution having a pH of 7 anda temperature of 37° C., which is at least 10% higher than an activityof native α-galactosidase immediately upon subjecting the nativeα-galactosidase to an aqueous solution having a pH of 7 and atemperature of 37° C.; and

(i) a circulating half-life in a physiological system which is higher byat least 20% than the circulating half-life of the nativeα-galactosidase.

According to an aspect of some embodiments of the present inventionthere is provided a multimeric protein structure comprising at least twoα-galactosidase monomers being covalently linked to one another via alinking moiety, wherein the linking moiety is not present in nativeα-galactosidase.

According to an aspect of some embodiments of the present inventionthere is provided a pharmaceutical composition comprising a multimericprotein structure as described herein and a pharmaceutically acceptablecarrier.

According to an aspect of some embodiments of the present inventionthere is provided a method of treating Fabry disease, the methodcomprising administering to a subject in need thereof a therapeuticallyeffective amount of a multimeric protein structure as described herein,thereby treating the Fabry disease.

According to an aspect of some embodiments of the present inventionthere is provided a process of preparing a multimeric protein structureas described herein, the process comprising reacting α-galactosidasewith a cross-linking agent which comprises the linking moiety describedherein and at least two reactive groups.

According to some embodiments of the invention, the linking moietydescribed herein is not present in native α-galactosidase.

According to some embodiments of the invention, the multimeric proteinstructure features a characteristic selected from the group consistingof:

(a) an α-galactosidase activity, upon subjecting the multimeric proteinstructure to human plasma conditions for one hour, which is at least 10%higher than an activity of native α-galactosidase upon subjecting thenative α-galactosidase to human plasma conditions for one hour;

(b) an α-galactosidase activity which decreases upon subjecting themultimeric protein structure to human plasma conditions for one hour bya percentage which is at least 10% less than the percentage by which anactivity of the native α-galactosidase decreases upon subjecting thenative α-galactosidase to human plasma conditions for one hour;

(c) an α-galactosidase activity which remains substantially unchangedupon subjecting the multimeric protein structure to human plasmaconditions for one hour;

(d) an α-galactosidase activity, upon subjecting the multimeric proteinstructure to lysosomal conditions for one week, which is at least 10%higher than an activity of native α-galactosidase upon subjecting thenative α-galactosidase to lysosomal conditions for one week;

(e) an α-galactosidase activity which decreases upon subjecting themultimeric protein structure to lysosomal conditions for one day by apercentage which is at least 10% less than the percentage by which anactivity of the native α-galactosidase decreases upon subjecting thenative α-galactosidase to lysosomal conditions for one day;

(f) an α-galactosidase activity which remains substantially unchangedupon subjecting the multimeric protein structure to lysosomal conditionsfor one day;

(g) an α-galactosidase activity, immediately upon subjecting themultimeric protein structure to lysosomal conditions, which is at least10% higher than an activity of native α-galactosidase immediately uponsubjecting the native α-galactosidase to lysosomal conditions;

(h) an α-galactosidase activity, immediately upon subjecting themultimeric protein structure to an aqueous solution having a pH of 7 anda temperature of 37° C., which is at least 10% higher than an activityof native α-galactosidase immediately upon subjecting the nativeα-galactosidase to an aqueous solution having a pH of 7 and atemperature of 37° C.; and

(i) a circulating half-life in a physiological system which is higherthan a circulating half-life of the native α-galactosidase.

According to some embodiments of the invention, the α-galactosidaseactivity of the multimeric protein structure which remains substantiallyunchanged upon subjecting the multimeric protein structure to lysosomalconditions for one day, further remains substantially unchanged uponsubjecting the multimeric protein structure to lysosomal conditions forone week.

According to some embodiments of the invention, the circulatinghalf-life of the multimeric protein structure which is higher than acirculating half-life of the native α-galactosidase, is higher by atleast 20% than the circulating half-life of the native α-galactosidase.

According to some embodiments of the invention, the circulatinghalf-life of the multimeric protein structure which is higher than acirculating half-life of the native α-galactosidase, is higher by atleast 50% than the circulating half-life of the native α-galactosidase.

According to some embodiments of the invention, the multimeric proteinstructure is characterized by an α-galactosidase activity in an organupon administration of the multimeric protein structure to a vertebrate,the organ being selected from the group consisting of a spleen, a heartand a kidney.

According to some embodiments of the invention, the multimeric proteinstructure comprises two α-galactosidase monomers, the protein structurebeing a dimeric protein structure.

According to some embodiments of the invention, the α-galactosidase is ahuman α-galactosidase.

According to some embodiments of the invention, the α-galactosidase is aplant recombinant α-galactosidase.

According to some embodiments of the invention, the α-galactosidase hasan amino acids sequence selected from the group consisting of SEQ IDNO:1, SEQ ID NO:2 and SEQ ID NO:3.

According to some embodiments of the invention, the α-galactosidase isan alkaline α-galactosidase.

According to some embodiments of the invention, the α-galactosidase isan acid α-galactosidase.

According to some embodiments of the invention, the linking moietycomprises a poly(alkylene glycol).

According to some embodiments of the invention, the poly(alkyleneglycol) comprises at least two functional groups, each functional groupforming a covalent bond with one of the α-galactosidase monomers.

According to some embodiments of the invention, the at least twofunctional groups are terminal groups of the poly(alkylene glycol).

According to some embodiments of the invention, the at least one linkingmoiety has a general formula:—X₁—(CR₁R₂—CR₃R₄—Y)n-X₂—

wherein each of X₁ and X₂ is a functional group that forms a covalentbond with at least one α-galactosidase monomer;

-   -   Y is O, S or NR₅;    -   n is an integer from 1 to 200; and

each of R₁, R₂, R₃, R₄ and R₅ is independently selected from the groupconsisting of hydrogen, alkyl, cycloalkyl, alkenyl, alkynyl, alkoxy,hydroxy, oxo, thiol and thioalkoxy.

According to some embodiments of the invention, at least one of thefunctional groups forms an amide bond with an α-galactosidase monomer.

According to some embodiments of the invention, n is an integer from 5to 150.

According to some embodiments of the invention, n is an integer from 40to 70.

According to some embodiments of the invention, the pharmaceuticalcomposition further comprises a galactose.

According to some embodiments of the invention, the multimeric proteinstructure is for use as a medicament.

According to some embodiments of the invention, the medicament is fortreating Fabry disease.

According to some embodiments of the invention, the multimeric proteinstructure is for use in treating Fabry disease.

According to some embodiments of the invention, the process comprisesreacting dimeric α-galactosidase with the cross-linking agent.

According to some embodiments of the invention, the reactive groupscomprise a leaving group.

According to some embodiments of the invention, the reactive groupreacts with an amine group to form an amide bond.

According to some embodiments of the invention, each of the reactivegroups is capable of forming a covalent bond between the linking moietyand at least one α-galactosidase monomer.

According to some embodiments of the invention, a molar ratio of thecross-linking agent to monomers of α-galactosidase is in a range of from5:1 to 500:1.

According to some embodiments of the invention, the molar ratio is in arange of from 75:1 to 300:1.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 is a graph showing the activity of Fabrazyme® α-GAL, Replagal®α-GAL and plant recombinant human α-GAL-I, as a function of incubationtime under simulated lysosomal conditions (citrate phosphate buffer, pH4.6, 37° C.);

FIG. 2 is a graph showing the activity of Fabrazyme® α-GAL, Replagal®α-GAL, plant recombinant human α-GAL-I, and plant recombinant α-GAL-Iwith galactose (100 mg/mL), as a function of incubation time undersimulated physiological conditions (pH 7.4, 37° C.);

FIG. 3 is a graph showing the activity of Fabrazyme® α-GAL, Replagal®α-GAL and plant recombinant human α-GAL-I, as a function of incubationtime in human plasma at 37° C.;

FIG. 4 is a graph showing the activity of Fabrazyme® α-GAL, Replagal®α-GAL, plant recombinant human α-GAL-I, and plant recombinant α-GAL-Iwith galactose (100 mg/mL), as a function of incubation time undersimulated lysosomal conditions (citrate phosphate buffer, pH 4.6, 37°C.);

FIG. 5 is a scheme depicting the molecular structures of exemplarybis-N-hydroxysuccinimide-poly(ethylene glycol) (bis-NHS-PEG)cross-linking agents;

FIG. 6 is a scheme depicting a dimeric protein which has been reactedwith bis-NHS-PEG cross-linking agents;

FIG. 7 presents a scan of an SDS-PAGE gel showing plant recombinantα-GAL-I which was reacted with bis-NHS-PEG₅ (lanes 1-3), bis-NHS-PEG₈(lanes 7-9), and bis-NHS-PEG₄₅ (lanes 4-6), at a molar ratio of 50:1(lanes 1, 4 and 7), 100:1 (lanes 2, 5 and 8) and 200:1 (lanes 3, 6 and9) bis-NHS-PEG:α-GAL, as well as molecular weight markers (Mw) andnon-reacted plant recombinant α-GAL-I standard (Std) (arrows show theband comprising an α-GAL dimer);

FIG. 8 presents a scan of an isoelectric focusing gel showing plantrecombinant α-GAL-I which was reacted with bis-NHS-PEG₅ (lanes 1-3),bis-NHS-PEG₈ (lanes 7-9), and bis-NHS-PEG₄₅ (lanes 4-6), at a molarratio of 50:1 (lanes 1, 4 and 7), 100:1 (lanes 2, 5 and 8) and 200:1(lanes 3, 6 and 9) bis-NHS-PEG:α-GAL, as well as pH markers (M) andnon-reacted plant recombinant α-GAL-I standard (Std) (arrows show pHvalues for various bands);

FIG. 9 is a MALDI-TOF mass spectroscopy spectrum of plant recombinantα-GAL-I cross-linked by bis-NHS-PEG₄₅ (x-axis indicates m/z values, andm/z values of peaks are shown);

FIG. 10 is a MALDI-TOF mass spectroscopy spectrum of plant recombinantα-GAL-I cross-linked by bis-NHS-PEG₈ (x-axis indicates m/z values, andm/z values of peaks are shown);

FIG. 11 presents a photograph showing the α-GAL substrateN-dodecanoyl-nitrobenzoxadiazole-ceramide trihexoside (Gb₃-NBD) and theα-GAL reaction product lactosyl ceramide-nitrobenzoxadiazole (lactosylceramide-NBD), as visualized by irradiation under UV light (365 nm)following high performance thin layer chromatography, followingincubation of the substrate Gb₃-NBD with plant recombinant human α-GAL-Icross-linked with bis-NHS-PEG₄₅ (left lane), Replagal® α-GAL (middlelane) and without α-GAL (right lane);

FIGS. 12A, 12B and 12C, are graphs showing the activity of Fabrazyme®α-GAL, Replagal® α-GAL, plant recombinant human α-GAL-I, and plantrecombinant human α-GAL-I cross-linked with bis-NHS-PEG₅ (FIG. 12A),bis-NHS-PEG₈ (FIG. 12B) and bis-NHS-PEG₄₅ (FIG. 12C) at a molar ratio of50:1 (“1” in FIG. 12A, “7” in FIG. 12B and “4” in FIG. 12C), 100:1 (“2”in FIG. 12A, “8” in FIG. 12B and “5” in FIG. 12C) and 200:1 (“3” in FIG.12A, “9” in FIG. 12B and “6” in FIG. 12C) bis-NHS-PEG:α-GAL as afunction of incubation time under simulated lysosomal conditions(citrate phosphate buffer, pH 4.6, 37° C.);

FIG. 13 is a graph showing the pharmacokinetic profile of Replagal®α-GAL, plant recombinant human α-GAL-I, and plant recombinant humanα-GAL-I cross-linked with bis-NHS-PEG₄₅ in the plasma of Fabry mice; theresidual activity of each α-GAL is presented as a percentage of themaximal residual activity of each α-GAL, as a function of time followinginjection of the α-GALs;

FIGS. 14A and 14B present a graph (FIG. 14A) showing the activity ofReplagal® α-GAL, plant recombinant human α-GAL-I (prh-alpha-GAL-I), andplant recombinant human α-GAL-I cross-linked with bis-NHS-PEG₈(prh-alpha-GAL-I-CL8) or bis-NHS-PEG₄₅ (prh-alpha-GAL-I-CL45) in thespleens of Fabry mice 2 hours following injection of α-GAL, and aphotograph of a Western blot (FIG. 14B) showing Replagal® α-GAL (lanes10-12 and 15), plant recombinant human α-GAL-I (lanes 7-9 and 13), andplant recombinant human α-GAL-I cross-linked with bis-NHS-PEG₈ (lanes4-6) or bis-NHS-PEG₄₅ (lanes 1-3 and 14) in the spleens of Fabry micefollowing injection of α-GAL (lanes 1-12) or as a standard consisting of50 ng α-GAL (lanes 13-15);

FIGS. 15A and 15B present a graph (FIG. 15A) showing the activity ofReplagal® α-GAL, plant recombinant human α-GAL-I (prh-alpha-GAL-I), andplant recombinant human α-GAL-I cross-linked with bis-NHS-PEG₈(prh-alpha-GAL-I-CL8) or bis-NHS-PEG₄₅ (prh-alpha-GAL-I-CL45) in thelivers of Fabry mice 2 hours following injection of α-GAL, and aphotograph of a Western blot (FIG. 15B) showing Replagal® α-GAL (lanes10-12 and 15), plant recombinant human α-GAL-I (lanes 7-9 and 13), andplant recombinant human α-GAL-I cross-linked with bis-NHS-PEG₈ (lanes4-6) or bis-NHS-PEG₄₅ (lanes 1-3 and 14) in the livers of Fabry micefollowing injection of α-GAL (lanes 1-12) or as a standard consisting of50 ng α-GAL (lanes 13-15);

FIG. 16 is a graph showing the activity of Replagal® α-GAL, plantrecombinant human α-GAL-I (prh-alpha-GAL-I), and plant recombinant humanα-GAL-I cross-linked with bis-NHS-PEG₈ (prh-alpha-GAL-I-) orbis-NHS-PEG₄₅ (prh-alpha-GAL-I-CL45) in the hearts of Fabry mice 2 hoursfollowing injection of α-GAL;

FIG. 17 is a graph showing the activity of Replagal® α-GAL, plantrecombinant human α-GAL-I (prh-alpha-GAL-I), and plant recombinant humanα-GAL-I cross-linked with bis-NHS-PEG₈ (prh-alpha-GAL-I-CL8) orbis-NHS-PEG₄₅ (prh-alpha-GAL-I-CL45) in the kidneys of Fabry mice 2hours following injection of α-GAL;

FIG. 18 is a graph showing the activity of Replagal® α-GAL and plantrecombinant human α-GAL-I (prh-alpha-GAL-I), and plant recombinant humanα-GAL-I cross-linked with bis-NHS-PEG₄₅ (prh-alpha-GAL-I-CL45) in thespleens of Fabry mice 2 hours, 24 hours, 3 days and 7 days followinginjection of α-GAL (endogenous wild type α-GAL (WT) is shown as astandard);

FIG. 19 is a graph showing the activity of Replagal® α-GAL and plantrecombinant human α-GAL-I (prh-alpha-GAL-I), and plant recombinant humanα-GAL I cross-linked with bis-NHS-PEG₄₅ (prh-alpha-GAL-I-CL45) in thelivers of Fabry mice 2 hours, 24 hours, 3 days and 7 days followinginjection of α-GAL (endogenous wild type α-GAL (WT) is shown as astandard);

FIG. 20 is a graph showing the activity of Replagal® α-GAL and plantrecombinant human α-GAL-I (prh-alpha-GAL-I), and plant recombinant humanα-GAL-I cross-linked with bis-NHS-PEG₄₅ (prh-alpha-GAL-I-CL45) in thehearts of Fabry mice 2 hours, 24 hours, 3 days and 7 days followinginjection of α-GAL (endogenous wild type α-GAL (WT) is shown as astandard);

FIG. 21 is a graph showing the activity of Replagal® α-GAL and plantrecombinant human α-GAL-I (prh-alpha-GAL-I), and plant recombinant humanα-GAL-I cross-linked with bis-NHS-PEG₄₅ (prh-alpha-GAL-I-CL45) in thekidneys of Fabry mice 2 hours, 24 hours, 3 days and 7 days followinginjection of α-GAL (endogenous wild type α-GAL (WT) is shown as astandard);

FIG. 22 presents a photograph of an image of an SDS-PAGE gel showingReplagal® mammalian recombinant human α-GAL (left lane), and Replagal®mammalian recombinant human α-GAL which was reacted with bis-NHS-PEG₄₅(middle lane), as well as molecular weight markers (right lane;molecular weights of markers are indicated in KDa units);

FIG. 23 presents a photograph of an isoelectric focusing gel showingReplagal® mammalian recombinant human α-GAL (left lane), and Replagal®mammalian recombinant human α-GAL which was reacted with bis-NHS-PEG₄₅(middle lane), as well as pH markers (right lane);

FIGS. 24A and 24B are MALDI-TOF mass spectroscopy spectra of Replagal®mammalian recombinant human α-GAL (FIG. 24A), and Replagal® mammalianrecombinant human α-GAL cross-linked by bis-NHS-PEG₄₅ (x-axis indicatesm/z values, and m/z values (in Da units) of peaks are shown);

FIG. 25 is a Michaelis-Menten plot showing the velocity (V) ofhydrolysis of p-nitrophenyl-α-D-galactopyranoside (pNP-G) by Replagal®mammalian recombinant human α-GAL (Replagal) and Replagal® mammalianrecombinant human α-GAL cross-linked by bis-NHS-PEG₄₅ (Replagal CL45),as a function of pNP-G concentration;

FIGS. 26A and 26B are graphs showing the activity of Replagal® mammalianrecombinant human α-GAL (Replagal) and Replagal® mammalian recombinanthuman α-GAL cross-linked by bis-NHS-PEG₄₅ (Replagal-CL45) as a functionof incubation time under simulated lysosomal conditions (citratephosphate buffer, pH 4.6, 37° C.) (FIG. 26A) or in human plasma at 37°C. (FIG. 26B);

FIGS. 27A-27D are graphs showing the activity of Replagal® α-GAL (R) andReplagal® α-GAL cross-linked with bis-NHS-PEG₄₅ (R-CL45) in the spleens(FIG. 27A), livers (FIG. 27B), hearts (FIG. 27C) and kidneys (FIG. 27D)of Fabry mice 2 hours following injection of α-GAL;

FIGS. 28A-28D are graphs showing Gb₃ levels in the hearts (FIG. 28A),kidneys (FIG. 28B), livers (FIG. 28C) and spleens (FIG. 28D) of Fabrymice, as a function of time following injection of Replagal® α-GAL (R)or Replagal® α-GAL cross-linked with bis-NHS-PEG₄₅ (R-CL45);

FIGS. 29A and 29B present scans of SDS-PAGE gels showing plantrecombinant human α-GAL-II (FIGS. 29A and 29B, lane 2), and plantrecombinant human α-GAL-II which was reacted with bis-NHS-PEG₂₁ (FIG.29A, lane 3), bis-NHS-PEG₄₅ (FIG. 29A, lane 4) or bis-NHS-PEG₆₈ (FIG.29B, lane 3), as well as molecular weight markers (FIGS. 29A and 29B,lane 1; molecular weights of markers are indicated in KDa units);

FIGS. 30A-30C are MALDI-TOF mass spectroscopy spectra of plantrecombinant human α-GAL-II (FIG. 30A), and plant recombinant humanα-GAL-II cross-linked by bis-NHS-PEG₂₁ (FIG. 30B) or bis-NHS-PEG₄₅ (FIG.30C) (x-axis indicates m/z values, and m/z values (in Da units) of peaksare shown);

FIGS. 31A-31D are graphs showing the activity of Replagal® mammalianrecombinant human α-GAL (Replagal), plant recombinant human α-GAL-II(prh-alpha-GAL-II) and plant recombinant human α-GAL-II cross-linked bybis-NHS-PEG₂₁ (prh-alpha-GAL-II-CL21; FIGS. 31A and 31C), bis-NHS-PEG₄₅(prh-alpha-GAL-II-CL45; FIGS. 31A-31D) or bis-NHS-PEG₆₈(prh-alpha-GAL-II-CL68; FIGS. 31B and 31D) as a function of incubationtime under simulated lysosomal conditions (citrate phosphate buffer, pH4.6, 37° C.) (FIGS. 31A and 31B) or in human plasma at 37° C. (FIGS. 31Cand 31D) (data shown in FIGS. 31C and 31D are from differentexperiments);

FIGS. 32A and 32B are graphs showing the pharmacokinetic profiles ofReplagal® α-GAL (Replagal), plant recombinant human α-GAL-II(prh-alpha-GAL-II), and plant recombinant human α-GAL-II cross-linkedwith bis-NHS-PEG₄₅ (prh-alpha-GAL-II-CL45) in the plasma of Fabry mice;concentration of each α-GAL is presented as a function of time followinginjection of α-GAL (FIGS. 32A and 32B present the same data at differenttime frames);

FIGS. 33A-33L are graphs showing the activity of Replagal® α-GAL(Replagal), plant recombinant human α-GAL-II (prh-alpha-GAL-II) andplant recombinant human α-GAL-II cross-linked with bis-NHS-PEG₄₅(prh-alpha-GAL-II-CL45; FIGS. 33A-33L) or bis-NHS-PEG₂₁(prh-alpha-GAL-II-CL21; FIGS. 33E-33L) in the hearts (FIGS. 33A, 33E and33I), kidneys (FIGS. 33B, 33F and 33J), livers (FIGS. 33C, 33G and 33K)and spleens (FIGS. 33D, 33H and 33L) of Fabry mice 2 hours (FIGS.33A-33H), 7 days (FIGS. 33A-33D and 33I-33L), 14 days (FIGS. 33A-33D)and 28 days (FIGS. 33A-33D) following injection of α-GAL;

FIGS. 34A-34C are graphs showing the kinetic parameters V_(max) (FIG.34A), K_(M) (FIG. 34B) and k_(cat) (FIG. 34C) for plant recombinanthuman α-GAL-II (prh-alpha-GAL-II) and plant recombinant human α-GAL-IIcross-linked with bis-NHS-PEG₄₅ (prh-alpha-GAL-II-CL45), as a functionof pH;

FIG. 35 presents a scan of an SDS-PAGE gel showing plant recombinanthuman α-GAL-I (prh-α-Gal-I), and plant recombinant human α-GAL-I whichwas reacted with methoxy-capped NHS-PEG having a molecular weight of 2KDa (prh-α-Gal-I-PEG 2000), 5 KDa (prh-α-Gal-I-PEG 5000) or 10 KDa(prh-α-Gal-I-PEG 10000), as well as molecular weight markers (left lane;molecular weights of markers are indicated in KDa units);

FIGS. 36A and 36B are graphs showing the activity of Fabrazyme®mammalian recombinant human α-GAL (Fabrazyme), Replagal® mammalianrecombinant human α-GAL (Replagal), plant recombinant human α-GAL-I andplant recombinant human α-GAL-I which was reacted with methoxy-cappedNHS-PEG having a molecular weight of 2 KDa (α-Gal-I-PEG 2000), 5 KDa(α-Gal-I-PEG 5000) or 10 KDa (α-Gal-I-PEG 10000), as a function ofincubation time under simulated lysosomal conditions (citrate phosphatebuffer, pH 4.6, 37° C.) (FIG. 36A) or in human plasma at 37° C. (FIG.36B);

FIG. 37 presents a scan of an SDS-PAGE gel showing plant recombinantα-GAL-I which was reacted with bis-NHS-PEG₂ (lanes 1-3), bis-NHS-PEG₄(lanes 4-6), bis-NHS-PEG₆₈ (lanes 7-9), bis-NHS-PEG₁₅₀ (lanes 10-12) andbis-NHS-PEG₄₅ (CL45), at a molar ratio of 50:1 (lanes 1, 4, 7 and 10),100:1 (lanes 2, 5, 8 and 11) and 200:1 (lanes 3, 6, 9 and 12)bis-NHS-PEG:α-GAL, as well as molecular weight markers (MW);

FIG. 38 presents a scan of an SDS-PAGE gel showing plant recombinantα-GAL-I which was reacted with bis-COOH-PEG₁₂ (lanes 1-3),bis-COOH-PEG₂₈ (lanes 4-6), bis-COOH-PEG₄₅ (lanes 7-9), andbis-NHS-PEG₄₅ (CL45), at a molar ratio of 50:1 (lanes 1, 4 and 7), 100:1(lanes 2, 5 and 8) and 200:1 (lanes 3, 6 and 9) bis-NHS-PEG:α-GAL, aswell as molecular weight markers (MW), and non-crosslinked plantrecombinant α-GAL-I as a control (con);

FIG. 39 is a graph showing the activity of Replagal® α-GAL, plantrecombinant human α-GAL-I (prh-α-GAL-I), and plant recombinant humanα-GAL-I cross-linked with bis-NHS-PEG₄₅ (prh-α-GAL-I-CL45), bis-NHS-PEG₄(prh-α-GAL-I-CL4), bis-NHS-PEG₂ (prh-α-GAL-I-CL2), bis-COOH-PEG₄₅(prh-α-GAL-I-CLA45) bis-COOH-PEG₂₈ (prh-α-GAL-I-CLA28) or bis-COOH-PEG₁₂(prh-α-GAL-I-CLA12) as a function of incubation time under simulatedlysosomal conditions (citrate phosphate buffer, pH 4.6, 37° C.);

FIGS. 40A and 40B are graphs showing the activity of plant recombinanthuman α-GAL-II cross-linked by bis-NHS-PEG₄₅ as a function of incubationtime under simulated lysosomal conditions (citrate phosphate buffer, pH4.6, 37° C.) (FIG. 40A) or in human plasma at 37° C. (FIG. 40B) (FIG.40B shows the activity of Replagal® mammalian recombinant α-GAL andnon-cross-linked plant recombinant human α-GAL-II for comparison);

FIG. 41 presents a scan of an SDS-PAGE gel showing plant recombinantα-GAL-II from 3 different batches (lanes 1-3) and plant recombinantα-GAL-II which was reacted with bis-NHS-PEG₄₅ from 5 different batches(lanes 4-8), as well as molecular weight markers (MW);

FIG. 42 presents a scan of an isoelectric focusing gel showing plantrecombinant α-GAL-II from 3 different batches (lanes 1-3) and plantrecombinant α-GAL-II which was reacted with bis-NHS-PEG₄₅ from 5different batches (lanes 4-8), as well as pH markers (M);

FIGS. 43A-43F are MALDI-TOF mass spectroscopy spectra of plantrecombinant human α-GAL-II (FIG. 43A), and plant human α-GAL-IIcross-linked by bis-NHS-PEG₄₅ from 5 different batches (FIGS. 43B-43F,respectively) (x-axis indicates m/z values, and m/z values (in Da units)of peaks are shown); and

FIG. 44 is a graph showing the catalytic velocity (V) of α-GAL activityexhibited by plant human α-GAL-II cross-linked by bis-NHS-PEG₄₅ from 5different batches, as a function of substrate(p-nitrophenyl-α-D-galactopyranoside) concentration.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to novelmultimeric protein structures and, more particularly, but notexclusively, to multimeric protein structures of α-galactosidase and touses thereof in treating Fabry disease.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details set forth in the following description orexemplified by the Examples. The invention is capable of otherembodiments or of being practiced or carried out in various ways.

Deficiencies of a lysosomal protein (e.g., defects in a lysosomalprotein or absence of a lysosomal protein) can cause considerable harmto the health of a subject (a lysosomal storage disease). Enzymereplacement therapy (ERT), in which the deficient protein isadministered to a patient, has been used in attempts to treat lysosomalstorage diseases. However, administration of the deficient protein doesnot necessarily result in a considerable and/or persistent increase inthe activity of the protein in vivo.

Fabry disease is an example of an X-linked recessive (inherited)lysosomal storage disease which can cause a wide range of systemicsymptoms. A deficiency of the lysosomal enzyme α-galactosidase A due tomutation causes a glycolipid known as globotriaosylceramide (also knownas Gb₃ or ceramide trihexoside) to accumulate within the blood vessels,other tissues, and organs. This accumulation leads to an impairment oftheir proper function. Two enzyme replacement therapies (ERTs) areavailable to functionally compensate for α-galactosidase deficiency.Agalsidase alpha (Replagal®, Shire) and agalsidase beta (Fabrazyme®,Genzyme) are both recombinant forms of the human α-galactosidase Aenzyme. These enzymes are difficult to manufacture and as such areexpensive. Recently, contamination at Genzyme's Allston, Mass., plantcaused a worldwide shortage of agalsidase beta, and supplies wererationed to patients at one-third the recommended dose.

As shown herein, α-galactosidases exert their maximal activity at low pHlevels characteristic of lysosomes, while their activity at higher pHlevels is compromised. Thus, for example, α-galactosidase used in ERTwould have little ability to hydrolyze terminal galactosylatedglycolipids in the serum of Fabry patients.

Moreover, as further shown herein, even under lysosomal conditions, theactivity of α-galactosidases is gradually compromised, although at aslower rate than at higher pH levels.

Motivated by a need to solve the compromised activity ofα-galactosidases, the present inventors have searched for stabilizedforms of α-galactosidase (α-GAL). More specifically, the presentinventors have envisioned that a stabilized form of α-galactosidasewould exhibit longer lasting activity in general, including longerlasting activity in serum. The present inventors have thus designed andsuccessfully prepared and practiced stabilized forms of nativeα-galactosidase and have indeed shown that such stabilized forms exhibitan improved performance, in terms of enhanced activity and/or a longerlasting activity under both lysosomal conditions and in a serumenvironment, which allows for an enhanced activity of the protein invivo.

The present inventors have demonstrated a formation of stabilized formsof α-galactosidase which exhibit an improved performance by means ofcross-linking native α-galactosidase, via formation of new covalentlinkage between α-galactosidase monomers.

Referring now to the drawings, FIGS. 1 and 4 show the decline of enzymeactivity under lysosomal conditions for plant recombinant human α-GAL I(prh-α-GAL I) and Fabrazyme® and Replagal® α-GAL. FIGS. 2 and 3 show thedecline of enzyme activity under simulated physiological conditions orin human plasma, for the same α-GAL varieties. FIGS. 2 and 4 show thatgalactose decreases the rate of the decline in α-GAL activity.

FIG. 5 shows exemplary PEG (polyethylene glycol) cross-linking agents,according to optional embodiments of the invention. FIG. 6 depicts across-linked α-GAL dimer according to optional embodiments of theinvention.

FIGS. 7-10 and 37 show that prh-α-GAL-I reacted with exemplarycross-linking agents comprising N-hydroxysuccinimide moieties. FIG. 38shows that prh-α-GAL-I reacted with exemplary cross-linking agentscomprising carboxyl groups, following in situ activation withN-hydroxysuccinimide. FIGS. 7, 37 and 38 show that the reaction with thecross-linking agent resulted in α-GAL appearing primarily in a dimericform rather than a monomeric form under denaturing conditions,indicating that the quaternary structure of the α-GAL was maintained bycovalent cross-linking. FIG. 11 shows that the cross-linked α-GALretained its enzymatic activity.

FIGS. 12A-12C and 39 show that the cross-linked prh α-GAL-I exhibits alonger lasting activity than non-cross-linked α-GAL under simulatedlysosomal conditions. The increase in stability is stronger for PEG₂₈and PEG₄₅ linkers than for shorter PEG linkers. FIG. 13 shows that thecross-linked prh-α-GAL-I exhibits a longer lasting activity thannon-cross-linked α-GAL in plasma in vivo. FIGS. 14A-21 show thatcross-linked prh-α-GAL-I exhibits an enhanced activity in vivo in thespleen, liver, heart and kidneys. The enhancement of α-GAL activity isstronger for PEG₄₅ linkers than for shorter PEG linkers. FIGS. 15A, 15Band 19 show that although cross-linked prh-α-GAL-I exhibits an enhancedactivity in vivo, the enhanced activity is not as concentrated in theliver as is Replagal® α-GAL activity.

The above results indicate that cross-linking plant recombinant humanα-GAL-I results in a dimer with improved stability, which allows for amore effective increase of α-GAL activity when administered in vivo.

Similarly, FIGS. 22-28D show that cross-linking mammalian recombinanthuman α-GAL results in a covalently-linked dimer (FIGS. 22-24B), whichexhibits normal enzymatic activity (FIG. 25), as well as longer lastingactivity under both lysosomal conditions and in plama (FIGS. 26A-26B),and enhanced activity in vivo in the spleen, liver, heart and kidneys(FIGS. 27A-28D).

Similarly, FIGS. 29A-33L show that cross-linking plant recombinant humanα-GAL II results in a covalently-linked dimer (FIGS. 29-30), whichexhibits longer lasting activity under both lysosomal conditions and inplama (FIGS. 31A-31B), and enhanced activity in vivo in plasma and inthe spleen, liver, heart and kidneys (FIGS. 32A-33L). As shown in FIGS.33A-33L, cross-linking with a PEG₄₅ linker was particularly effective atenhancing in vivo activity.

These results indicate that the advantageous effects of cross-linkingare applicable to a variety of α-GAL proteins.

FIGS. 34A-34C show that cross-linking α-GAL enhances parameters of α-GALenzymatic catalysis, broadens the pH range for α-GAL activity, andallows for α-GAL activity at a pH of about 7 or more.

FIGS. 35-36B show that PEGylation without cross-linking has nosignificant effect on α-GAL activity, indicating that the advantageouseffects of cross-linking are specifically due to cross-linking, ratherthan to an effect of PEGylation.

FIGS. 40-44 show that cross-linking of α-GAL according to embodiments ofthe invention allows for good reproducibility of the stability (FIGS.40A-40B), degree of covalent cross-linking (FIGS. 41-43F) and enzymaticproperties (FIG. 44) of the cross-linked α-GAL.

The results presented herein show that covalently cross-linked,multimeric protein structures of α-galactosidase are characterized by ahigher stability and enhanced activity under physiologically relevantconditions, as compared to the native forms of α-galactosidase.

Thus, the covalently-linked multimeric protein structure may exhibit anactivity which is higher than an activity of a native form ofα-galactosidase, as a result of the activity of the native form decayingmore rapidly over time than the activity of the cross-linked multimericprotein structure, which is stabilized by the covalent cross-linking.

The covalently cross-linked multimeric protein structure may exhibit anactivity which is higher than an activity of a native form ofα-galactosidase, also due to a higher initial activity (e.g., due todifferent parameters of activity), i.e., independently of any decay ofactivity over time.

Hence, according to an aspect of some embodiments of the presentinvention there is provided a multimeric protein structure comprising atleast two α-galactosidase monomers being covalently linked to oneanother via a linking moiety. According to some embodiments, themultimeric protein structure features a stability higher than that ofnative α-galactosidase and/or an initial activity higher than that ofnative α-galactosidase, as described in detail below.

Herein, the term “monomer” with respect to α-galactosidase refers to anindividual polypeptide of α-galactosidase. The polypeptide may includenon-peptidic substituents (e.g., one or more saccharide moieties).

Herein, the term “native” with respect to α-galactosidase encompassesproteins comprising an amino acid sequence substantially identical(i.e., at least 95% homology, optionally at least 99% homology, andoptionally 100%) to an amino acid sequence of a naturally occurringα-galactosidase protein. A native α-galactosidase may be a proteinisolated from a natural source, or a recombinantly produced protein(e.g., derived from mammalian cells, plant cells, yeast cells, bacterialcells, insect cells).

The term “native”, when used in reference to a quaternary structure ofα-galactosidase (e.g., an α-galactosidase dimer), further comprises aquaternary structure substantially identical to that of a naturallyoccurring protein.

Herein, the phrase “naturally occurring protein” refers to a protein ina form which occurs in nature (e.g., in an organism), with respect tothe protein's amino acid sequence, as well as the protein's quaternarystructure if the protein is in a multimeric form.

Post-translational modifications (e.g., glycosylation) of naturallyoccurring α-galactosidase proteins (e.g., in an organism which expressesthe naturally occurring α-galactosidase protein) may be present, absentor modified in the native form of α-galactosidase referred to herein. Anative form of α-galactosidase (e.g., a recombinantly producedα-galactosidase) may optionally comprise different post-translationalmodifications than those of the naturally occurring α-galactosidase,provided that the native form of the α-galactosidase retains asubstantially similar amino acid sequence and structure as the naturallyoccurring α-galactosidase, as described hereinabove.

Herein, the native form of a protein may refer to a monomeric structure(e.g., an α-galactosidase monomer) and/or a multimeric structure (e.g.,an α-galactosidase dimer). For example, a dimeric protein can bedescribed as a native form of α-galactosidase, and a monomericpolypeptide in a dimeric protein can be described as a native form ofthe α-galactosidase monomer.

Optionally, the multimeric protein structure described herein is adimeric structure, as is the native form of α-galactosidase.

Alternatively, the multimeric protein structure comprises more than twoα-galactosidase monomers. For example, the multimeric protein structuremay be a tetramer, a hexamer, or an octamer comprised of α-galactosidasemonomers.

The multimeric protein structures described herein comprise covalentbonds which link the α-galactosidase monomers therein, and which areabsent from the native form of the α-galactosidase.

Optionally, the linking moiety which links the α-galactosidase monomersis a moiety which is not present in a native form of α-galactosidase(e.g., a synthetic linking moiety).

Thus, for example, the linking moiety is optionally a moiety which iscovalently attached to a side chain, an N-terminus or a C-terminus, or amoiety related to post-translational modifications (e.g., a saccharidemoiety) of an α-galactosidase monomer, as well as to a side chain, anN-terminus or a C-terminus, or a moiety related to post-translationalmodifications (e.g., a saccharide moiety) of another α-galactosidasemonomer. Exemplary such linking moieties are described in detailhereinunder.

Alternatively, the linking moiety forms a part of the α-galactosidasemonomers being linked (e.g., a part of a side chain, N-terminus orC-terminus, or a moiety related to post-translational modifications(e.g., a saccharide moiety) of an α-galactosidase monomer, as well as ofa side chain, an N-terminus or a C-terminus, or a moiety related topost-translational modifications (e.g., a saccharide moiety) of anotherα-galactosidase monomer).

Thus, for example, the linking moiety can be a covalent bond (e.g., anamide bond) between a functional group of a side chain, N-terminus,C-terminus or moiety related to post-translational modifications of amonomer (e.g., an amine), and a complementary functional group of a sidechain, N-terminus, C-terminus or moiety related to post-translationalmodifications of another monomer (e.g., carboxyl), wherein such acovalent bond is absent from the native form of the α-galactosidase.Other covalent bonds, such as, for example, an ester bond (between ahydroxy group and a carboxyl); a thioester bond; an ether bond (betweentwo hydroxy groups); a thioether bond; an anhydride bond (between twocarboxyls); a thioamide bond; a carbamate or thiocarbamate bond, arealso contemplated.

Optionally, the linking moiety is devoid of a disulfide bond. However, alinking moiety which includes a disulfide bond at a position which doesnot form a link between monomers (e.g., cleavage of the disulfide bonddoes not cleave the link between the monomers) is within the scope ofthis embodiment of the invention. A potential advantage of linkingmoiety devoid of a disulfide bond is that it is not susceptible tocleavage by mildly reducing conditions, as are disulfide bonds.

Optionally, the linking moiety is a non-peptidic moiety (e.g., thelinking moiety does not consist of an amide bond, an amino acid, adipeptide, a tripeptide, an oligopeptide or a polypeptide).

Alternatively, the linking moiety may be, or may comprise, a peptidicmoiety (e.g., an amino acid, a dipeptide, a tripeptide, an oligopeptideor a polypeptide).

Optionally, the linking moiety is not merely a linear extension of anyof the α-galactosidase monomers attached thereto (i.e., the N-terminusand C-terminus of the peptidic moiety is not attached directly to theC-terminus or N-terminus of any of the α-galactosidase monomers).

Alternatively, the linking moiety is formed by direct covalentattachment of an N-terminus of an α-galactosidase monomer with aC-terminus of another α-galactosidase monomer, so as to produce a fusedpolypeptide. Such a polypeptide will not be a native form ofα-galactosidase, although it may comprise two α-galactosidase monomersessentially in their native form.

However, the covalent linking of α-galactosidase monomers describedherein is preferably in a form other than direct linkage of anN-terminus to a C-terminus.

The linking moiety is also referred to herein as a cross-linking moiety.The linking of α-galactosidase monomers by a linking moiety is referredto herein as “cross-linking”.

The cross-linking moiety can be a covalent bond, a chemical atom orgroup (e.g., a C(═O)—O— group, —O—, —S—, NR—, —N═N—, —NH—C(═O)—NH—, andthe like) or a bridging moiety (composed of a chain of chemical groups).

A bridging moiety can be, for example, a polymeric or oligomeric group.

The bridging moiety is a multifunctional moiety (e.g., biradical,triradical, etc.) that is attached to side chains, moieties related topost-translational modifications (e.g., saccharide moieties) and/ortermini (i.e., N-termini, C-termini) of two or more of the monomers.

As exemplified herein in the Examples section, relatively short linkingmoieties (e.g., PEG₂, PEG₄, PEG₅) may be less effective than longerlinking moieties (e.g., PEG₂₈, PEG₄₅) at cross-linking between differentα-galactosidase monomers.

Hence, according to some embodiments, the linking moiety is not acovalent bond, a chemical atom or group, but is rather a bridgingmoiety.

Hence, according to some embodiments, the linking moiety is at least 10atoms long, optionally at least 20 atoms long, optionally at least 30atoms long, optionally at least 50 atoms long, optionally at least 100atoms long, and optionally at least 200 atoms long.

Herein, the length of a linking moiety (when expressed as a number ofatoms) refers to length of the backbone of the linking moiety, i.e., thenumber atoms forming a linear chain between residues of each of twomonomers linked via the linking moiety.

Optionally, the linking moiety is below a certain size, so as to avoidan unnecessarily excessive part of the linking moiety in the formedcross-linked protein, which may interfere with the function of theprotein.

Hence, according to some embodiments, each linking moiety ischaracterized by a molecular weight of less than 20 KDa, optionally lessthan 10 KDa, optionally less than 5 KDa, and optionally less than 3 KDa.

In order to facilitate cross-linking, the linking moiety is optionallysubstantially flexible, wherein the bonds in the backbone of the linkingmoiety are mostly rotationally free, for example, single bonds which arenot coupled to a double bond (e.g., unlike an amide bond) and whereinrotation is not sterically hindered. Optionally, at least 70%,optionally at least 80%, and optionally at least 90% (e.g., 100%) of thebonds in the backbone of the linking moiety are rotationally free.

In some embodiments, the linking moiety comprises a poly(alkyleneglycol) chain.

The phrase “poly(alkylene glycol)”, as used herein, encompasses a familyof polyether polymers which share the following general formula:—O—[(CH₂)_(m)—O—]_(n)-, wherein m represents the number of methylenegroups present in each alkylene glycol unit, and n represents the numberof repeating units, and therefore represents the size or length of thepolymer. For example, when m=2, the polymer is referred to as apolyethylene glycol, and when m=3, the polymer is referred to as apolypropylene glycol.

In some embodiments, m is an integer greater than 1 (e.g., m=2, 3, 4,etc.).

Optionally, m varies among the units of the poly(alkylene glycol) chain.For example, a poly(alkylene glycol) chain may comprise both ethyleneglycol (m=2) and propylene glycol (m=3) units linked together.

The poly(alkylene glycol) optionally comprises at least two functionalgroups (e.g., as described herein), each functional group forming acovalent bond with one of the α-galactosidase monomers. The functionalgroups are optionally terminal groups of the poly(alkylene glycol), suchthat the entire length of the poly(alkylene glycol) lies between the twofunctional groups.

The phrase “poly(alkylene glycol)” also encompasses analogs thereof, inwhich the oxygen atom is replaced by another heteroatom such as, forexample, S, —NH— and the like. This term further encompasses derivativesof the above, in which one or more of the methylene groups composing thepolymer are substituted. Exemplary substituents on the methylene groupsinclude, but are not limited to, alkyl, cycloalkyl, alkenyl, alkynyl,alkoxy, hydroxy, oxo, thiol and thioalkoxy, and the like.

The phrase “alkylene glycol unit”, as used herein, encompasses a—(CH₂)_(m)—O— group or an analog thereof, as described hereinabove,which forms the backbone chain of the poly(alkylene glycol), wherein the(CH₂)_(m) (or analog thereof) is bound to a heteroatom belonging toanother alkylene glycol unit or to an α-galactosidase monomer moiety (incases of a terminal unit), and the O (or heteroatom analog thereof) isbound to the (CH₂)_(m) (or analog thereof) of another alkylene glycolunit, or to a functional group which forms a bond with anα-galactosidase monomer.

An alkylene glycol unit may be branched, such that it is linked to 3 ormore neighboring alkylene glycol units, wherein each of the 3 or moreneighboring alkylene glycol units are part of a poly(alkylene glycol)chain. Such a branched alkylene glycol unit is linked via the heteroatomthereof to one neighboring alkylene glycol unit, and heteroatoms of theremaining neighboring alkylene glycol units are each linked to a carbonatom of the branched alkylene glycol unit. In addition, a heteroatom(e.g., nitrogen) may bind more than one carbon atom of an alkyleneglycol unit of which it is part, thereby forming a branched alkyleneglycol unit (e.g., [(—CH₂)_(m)]₂N— and the like).

In exemplary embodiments, at least 50% of alkylene glycol units areidentical, e.g., they comprise the same heteroatoms and the same mvalues as one another. Optionally, at least 70%, optionally at least90%, and optionally 100% of the alkylene glycol units are identical. Inexemplary embodiments, the heteroatoms bound to the identical alkyleneglycol units are oxygen atoms. In further exemplary embodiments, m is 2for the identical units.

In one embodiment, the linker is a single, straight chain linker,preferably being polyethylene glycol (PEG).

As used herein, the term “poly(ethylene glycol)” describes apoly(alkylene glycol), as defined hereinabove, wherein at least 50%, atleast 70%, at least 90%, and preferably 100%, of the alkylene glycolunits are —CH₂CH₂—O—. Similarly, the phrase “ethylene glycol units” isdefined herein as units of —CH₂CH₂O—.

According to optional embodiments, the linking moiety comprises apoly(ethylene glycol) or analog thereof, having a general formula:—X₁—(CR₁R₂—CR₃R₄—Y)_(n)—X₂—

wherein each of X₁ and X₂ is a functional group (e.g., as describedherein) that forms a covalent bond with at least one α-galactosidasemonomer;

Y is O, S or NR₅ (optionally O);

n is an integer, optionally from 1 to 200 (optionally from 5 to 150, andoptionally from 40 to 70), although higher values of n are alsocontemplated; and

each of R₁, R₂, R₃, R₄, and R₅ is independently selected from the groupconsisting of hydrogen, alkyl, cycloalkyl, alkenyl, alkynyl, alkoxy,hydroxy, oxo, thiol and thioalkoxy.

In some embodiments, n is at least 5, optionally at least 8, optionallyat least 15, optionally at least 25, and optionally at least 40.

In some embodiments, n is no more than 200, optionally no more than 150,and optionally no more than 70.

The poly(ethylene glycol) or analog thereof may optionally comprise acopolymer, for example, wherein the CR₁R₂—CR₃R₄—Y units in the aboveformula are not all identical to one another.

In some embodiments, at least 50% of CR₁R₂—CR₃R₄—Y units are identical.Optionally, at least 70%, optionally at least 90%, and optionally 100%of the CR₁R₂—CR₃R₄—Y units are identical.

Optionally, the linking moiety is branched, for example, such that forone or more CR₁R₂—CR₃R₄—Y units in the above formula, at least of one ofR₁, R₂, R₃, R₄, and R₅ is —(CR₁R₂—CR₃R₄—Y)_(p)—X₃—, wherein R₁-R₄ and Yare as defined hereinabove, p is an integer as defined herein for n(e.g., from 1 to 200), and X₃ is as defined herein for X₁ and X₂.

The functional groups may optionally form a bond such as, but notlimited to, an amide bond, an amide bond, an ester bond, and/or an etherbond.

For example, the functional group may optionally comprise a carbonylgroup which forms an amide bond with a nitrogen atom in a polypeptide(e.g., in a lysine residue or N-terminus), or an ester bond with anoxygen atom in a polypeptide (e.g., in a serine, threonine or tyrosineresidue).

Alternatively or additionally, the functional group may optionallycomprise a heteroatom (e.g., N, S, O) which forms an amide bond, esterbond or thioester bond with a carbonyl group in a polypeptide (e.g., ina glutamate or aspartate residue or in a C-terminus).

Alternative or additionally, the functional group may comprise an alkylor aryl group attached to a polypeptide (e.g., to a heteroatom in thepolypeptide).

Alternatively or additionally, the functional group may optionallycomprise a nitrogen atom which forms an amine bond with an alkyl groupin an α-galactosidase monomer, or an α-galactosidase monomer mayoptionally comprise a nitrogen atom which forms an amine bond with analkyl group in the functional group. Such an amine bond may be formed byreductive amination (e.g., as described hereinbelow).

In some embodiments, at least one of the functional groups forms anamide bond with a polypeptide (e.g., with a lysine residue therein).

The functional groups may be identical to one another or different.

In some embodiments, at least one of the functional groups is attachedto one functionality of a polypeptide (e.g., an amine group of a lysineresidue or N-terminus), and at least one of the functional groups isattached to a different functionality of a polypeptide (e.g., a thiolgroup of a cysteine residue).

According to optional embodiments, the multimeric protein structuredescribed herein exhibits a high stability in human plasma conditionsand/or in lysosomal conditions.

As used herein, the phrase “human plasma conditions” refers to humanplasma as a medium, at a temperature of 37° C.

As used herein, the phrase “lysosomal conditions” refers to an aqueoussolution having a pH of 4.6 as a medium (e.g., a citrate phosphatebuffer described herein), at a temperature of 37° C.

Enhanced stability under lysosomal conditions is advantageous becausethe lysosome is a target for replacement therapy for α-galactosidase, aslysosomes are the normal location for α-galactosidase activity in abody, and lysosomal conditions (e.g., acidic pH) represent optimalconditions for activity of α-galactosidase.

Without being bound by any particular theory, it is believed thatenhanced stability in serum-like conditions (e.g., the human plasmaconditions described herein) is also advantageous because stableα-galactosidase in the blood can act on metabolites (e.g., Gb₃) presentin the blood due to efflux from cells. A serum-active multimeric proteinstructure could optionally be efficient in removing and preventingglycosphinglipids deposited within blood vessel walls which promoteinflammation [Bodary et al., TCM 17(4):129-133]. For example, in Fabrydisease, the major pathogenesis results from the accumulation of Gb₃ inthe vascular endothelium, leading to vascular occlusion of smallvessels, ischemia and infarction of these vessels and ischemia andinfarction of the kidney, heart and brain [Desnick et al., 2003, Annalsof Internal Medicine, 138(4):338-346]. Additionally, enhanced stabilityin serum can negate the need for lysosomal trafficking. ERT can therebybecome much more accessible, as robust cost-effective host systems e.g.,plants, can be employed.

According to optional embodiments, the high stability of the multimericprotein structure in human plasma conditions is such that the multimericprotein structure exhibits, upon being subjected to human plasmaconditions for one hour, an α-galactosidase activity which is at least10% higher, optionally 20% higher, optionally 50% higher, and optionally100% higher, than an α-galactosidase activity of native α-galactosidaseupon subjecting the native α-galactosidase to the human plasmaconditions for one hour.

Alternatively or additionally, the high stability of the multimericprotein structure in human plasma conditions is such that anα-galactosidase activity of the multimeric protein structure decreasesmore slowly in human plasma conditions than a corresponding activity ofthe native α-galactosidase. Optionally, the multimeric protein structureexhibits an activity which decreases upon subjecting the proteinstructure to human plasma conditions for one hour by a percentage whichis at least 10% less, optionally 20% less, optionally 50% less, andoptionally 80% less, than the percentage by which a correspondingactivity of the native α-galactosidase decreases upon subjecting thenative α-galactosidase to human plasma conditions for one hour.

It is to be understood that herein, a decrease which is “10% less” thana decrease of 50% refers to a decrease of 45% (45 being 10% less than50), and not to a decrease of 40% (50%-10%).

Alternatively or additionally, the high stability of the multimericprotein structure in human plasma conditions is such that anα-galactosidase activity of the multimeric protein structure remainssubstantially unchanged upon subjecting the multimeric protein structureto human plasma conditions for one hour, and optionally for 2, 4 or even6 hours.

As used herein, the phrase “substantially unchanged” refers to a level(e.g., of activity) which remains in a range of from 50% to 150% of theinitial level, and optionally a level which remains at least 60%,optionally at least 70%, optionally at least 80%, and optionally atleast 90% of the initial level.

Optionally, the high stability of the multimeric protein structure inlysosomal conditions is such that the multimeric protein structureexhibits, upon being subjected to lysosomal conditions for apredetermined time period (e.g., one day, two days, 3 days, one week),an α-galactosidase activity which is at least 10% higher, optionally 20%higher, optionally 50% higher, and optionally 100% higher, than anactivity of native α-galactosidase upon subjecting the nativeα-galactosidase to the lysosomal conditions for the same predeterminedtime period.

Alternatively or additionally, the high stability of the multimericprotein structure in lysosomal conditions is such that anα-galactosidase activity of the multimeric protein structure decreasesmore slowly in lysosomal conditions than a corresponding activity of thenative α-galactosidase. Optionally, the multimeric protein structureexhibits an activity which decreases upon subjecting the proteinstructure to lysosomal conditions for a predetermined time period (e.g.,one day, 2 days, 3 days, one week), by a percentage which is at least10% less, optionally 20% less, optionally 50% less, and optionally 80%less, than the percentage by which a corresponding activity of thenative α-galactosidase decreases upon subjecting the nativeα-galactosidase to lysosomal conditions for the same time period.

Alternatively or additionally, the high stability of the multimericprotein structure in lysosomal conditions is such that anα-galactosidase activity of the multimeric protein structure remainssubstantially unchanged upon subjecting the multimeric protein structureto lysosomal conditions for one day, for 2 days, for 3 days, for oneweek, for two weeks, and/or for one month.

As exemplified in the Examples section herein, in addition to exhibitingmore stability over time, the multimeric protein structure may exhibitparameters of α-galactosidase activity which are different than those ofthe native α-galactosidase.

Hence, according to optional embodiments, the multimeric proteinstructure is characterized as exhibiting, independently of any decay ofactivity over time, an α-galactosidase activity which is higher than anα-galactosidase activity of a native form of the protein. Optionally,the activity is 10% higher, and optionally 20% higher, than thecorresponding activity of the native form.

In order to characterize such an activity, the activity is preferablydetermined immediately (e.g., within 1 hour, within 15 minutes) uponsubjecting the native α-galactosidase or multimeric protein structure toconditions (e.g., as described herein) in which the activity decreasessubstantially, so that the measured activity will reflect the activityper se, and not a degree of stability.

Optionally, the multimeric protein structure is characterized asexhibiting an α-galactosidase activity in lysosomal conditions which ishigher than a corresponding activity of native α-galactosidase.

Alternatively or additionally, the multimeric protein structure ischaracterized as exhibiting an α-galactosidase activity in simulatedphysiological conditions at a neutral pH which is higher than acorresponding activity of native α-galactosidase. The simulatedphysiological conditions comprise an aqueous solution (e.g., phosphatebuffer saline) at a temperature of 37° C. The pH is optionally 7.Alternatively, the pH is 7.4.

The α-galactosidase activity described herein is a biological activitywhich is characteristic of α-galactosidase (e.g., a catalytic activitycharacteristic of α-galactosidase, such as hydrolysis of a terminalα-galactosyl moiety of a substrate).

In some embodiments, a catalytic activity of α-galactosidase ischaracterized by a rate of catalysis at saturation (i.e., a V_(max)value).

Alternatively, the α-galactosidase activity is a therapeutic activity(e.g., an enzymatic activity having a therapeutic effect), such as atherapeutic activity in the context of Fabry disease. Optionally, thetherapeutic activity is determined in experimental animals (e.g., Fabrymice), and optionally in human Fabry patients.

Techniques for determining an activity of α-galactosidase will be knownto a skilled person. Typically, the α-galactosidase (i.e., the nativeform or a multimeric protein structure described herein) is contactedwith a compound recognized in the art as a substrate of α-galactosidase,and the degree of activity is then determined quantitatively. Compoundswhich allow for particularly convenient detection of α-galactosidaseactivity are known in the art and are commercially available.

In some embodiments, α-galactosidase activity is determined by assayinghydrolysis of 4-methylumbelliferyl-α-D-galactopyranoside (e.g., asdescribed in the Examples section herein).

In some embodiments, α-galactosidase activity is determined by assayinghydrolysis of p-nitrophenyl-α-D-galactopyranoside (e.g., as described inthe Examples section herein).

When comparing an activity of a multimeric protein structure describedherein with an activity of native α-galactosidase, the nativeα-galactosidase preferably comprises α-galactosidase monomerssubstantially identical (e.g., with respect to amino acid sequence andglycosylation pattern) to the α-galactosidase monomers of the multimericstructure.

According to some embodiments, the multimeric protein structure ischaracterized by a circulating half-life in a physiological system(e.g., blood, serum and/or plasma of a human or laboratory animal) whichis higher (e.g., at least 20%, at least 50% higher, at least 100%higher, at least 400% higher, at least 900% higher) than a circulatinghalf-life of native α-galactosidase.

An increased circulating half-life may optionally be associated with ahigher in vitro stability (e.g., as described herein), a higher in vivostability (e.g., resistance to metabolism) and/or with other factors(e.g., reduced renal clearance).

Circulating half-lives can be determined by taking samples (e.g., bloodsamples, tissue samples) from physiological systems (e.g., humans,laboratory animals) at various intervals, and determining a level ofα-galactosidase in the sample, using techniques known in the art.

Optionally, the half-life is calculated as a terminal half-life (e.g.,as described in the Examples section), wherein half-life is the timerequired for a concentration (e.g., a blood concentration) to decreaseby 50% after pseudo-equilibrium of distribution has been reached. Theterminal half-life may be calculated from a terminal linear portion of atime vs. log concentration, by linear regression of time vs. logconcentration (see, for example, Toutain & Bousquet-Melou [J VetPharmacol Ther 2004, 27:427-39]). Thus, the terminal half-life is ameasure of the decrease in drug plasma concentration due to drugelimination and not of decreases due to other reasons, and is notnecessarily the time necessary for the amount of the administered drugto fall by one half.

Determining a level of α-galactosidase (e.g., the multimeric proteinstructure or the native α-galactosidase) may comprise detecting thephysical presence of α-galactosidase (e.g., via an antibody againstα-galactosidase) and/or detecting a level of an α-galactosidase activity(e.g., as described herein).

According to some embodiments, the multimeric protein structure ischaracterized by an α-galactosidase activity in an organ (e.g., spleen,heart, kidney, brain, liver) upon administration (e.g., intravenousadministration) of the protein structure to a vertebrate (e.g., a human,a mouse), for example, a vertebrate with an α-galactosidase deficiency(e.g., a human Fabry disease patient, a Fabry mouse). Optionally, theα-galactosidase activity in the organ is higher than an α-galactosidaseactivity of native α-galactosidase in the organ, upon an equivalentadministration to a vertebrate.

The activity in an organ may be a function of uptake of theα-galactosidase and/or retention of α-galactosidase activity followinguptake.

Optionally, α-galactosidase activity in the organ is determined 2 hoursafter administration, and optionally 24 hours, optionally 3 days,optionally 7 days, and optionally 14 days, after administration.

As increased activity of α-galactosidase in a liver may in some cases beassociated with a lower activity in other parts of a body, and hence,with a reduced biological effect of the α-galactosidase.

Hence, in some embodiments, the multimeric protein structure ischaracterized by an enhanced α-galactosidase activity in an organ otherthan a liver. Exemplary organs include the spleen, heart and kidneys.

In some embodiments, the multimeric protein structure is characterizedby an enhanced α-galactosidase activity in an organ after administration(as described herein) which is at least 20% higher, optionally at least50% higher, optionally at least 100% higher, and optionally at least300% higher, than the activity of native α-galactosidase after anequivalent administration. As noted hereinabove, the present inventorshave devised and successfully prepared and practiced stabilized forms ofα-galactosidase by means of multimeric structures of cross-linkedα-galactosidase monomers.

Optionally, the α-galactosidase is a human α-galactosidase (e.g., arecombinant human α-galactosidase), for example, in order to facilitateoptimal biocompatibility for administration to human subjects. Humanα-galactosidase is commercially available, for example, as Replagal®(agalsidase alpha, Shire) and Fabrazyme® (agalsidase beta, Genzyme).

Herein, “human α-galactosidase” refers to an α-galactosidase comprisingan amino acid sequence substantially identical (e.g., as describedhereinabove) to an amino acid sequence of an α-galactosidase proteinwhich naturally occurs in humans.

In some embodiments, the α-galactosidase is a plant recombinantα-galactosidase. Exemplary α-galactosidases include plant recombinanthuman α-galactosidases.

Examples of α-GAL include, without limitation, α-GAL having an aminoacid sequence selected from the group consisting of SEQ ID NO: 1, SEQ IDNO: 2, and SEQ ID NO: 3. Optionally, the α-GAL has an amino acidsequence selected from the group consisting of SEQ ID NO: 2 and SEQ IDNO: 3.

As used herein, “α-galactosidase” refers to any protein which exhibitsan enzymatic activity (e.g., hydrolysis) towards galactose moieties inGb₃ (e.g., α-galactosidase A). Optionally, “α-galactosidase” refers toE.C. 3.2.1.22.

The α-galactosidase of embodiments of the invention can be purified(e.g., from plants or animal tissue) or generated by recombinant DNAtechnology.

As described herein, activity of α-galactosidase in serum may be highlyadvantageous, for example, for reducing Gb₃ levels in serum.

Hence, in some embodiments, the α-galactosidase is an alkalineα-galactosidase.

As used herein the phrase “alkaline α-galactosidase” refers to α-GALcharacterized by an ability to hydrolyse terminal-linked α-galactosemoieties from galactose-containing oligosaccharides under neutral tobasic pH conditions (e.g., about pH 7-7.5), particularly at a normalserum pH (e.g., about 7.35-7.45).

It will be appreciated that an alkaline α-GAL of some embodiments of theinvention may be active under neutral to basic pH conditions but maystill display activity under acidic pH conditions (i.e., about 4.6).

In a specific embodiment the enzyme is active under acidic to basic pHconditions (i.e., about pH 4.2-7.5).

In yet another specific embodiment the enzyme is active under pH ofabout 6.5-7.5.

Specific examples of alkaline α-galactosidases which can be used inaccordance with the present teachings are provided in US PatentApplication 20070036883, WO03/097791, and in PCT/IL2010/000956, each ofwhich is hereby incorporated by reference in its entirety.

Thus, alkaline α-galactosidase can be a member of the plant familyselected from the group consisting of Cucurbitaceae, Lamiaceae,Piperaceae, Solanaceae, Leguminosae, Cruciferae and Gramineae families.

According to a specific embodiment, the alkaline α-galactosidase is frommelon.

P.-R. Gaudreault and J. A. Webb have described in several publications,(such as “Alkaline alpha-galactosidase in leaves of Cucurbita pepo”,Plant Sci. Lett. 24, 281-288, 1982, “Partial purification and propertiesof an alkaline alpha-galactosidase from mature leaves of Cucurbitapepo”, Plant Physiol., 71, 662-668, 1983, and “Alkalinealpha-galactosidase activity and galactose metabolism in the familyCucurbitaceae”, Plant Science, 45, 71-75, 1986), a novel α-galactosidasepurified from young leaves of Cucurbita pepo, that has an optimalactivity at alkaline conditions (pH 7.5). In addition to the alkalineα-galactosidase, they also reported three acid forms of the enzyme, anddistinct substrate preferences were found for the acid and alkalineforms

α-Galactosidase activity at alkaline pH has been observed in othercucurbit tissue, such as cucumber fruit pedicels, young squash fruit andyoung melon fruit (“Melons: Biochemical and Physiological Control ofSugar Accumulation”, In: Encyclopedia of Agricultural Science, vol. 3,pp. 25-37, Arntzen, C. J., et al., eds. Academic Press, New York, 1994).

Bachmann et al. (“Metabolism of the raffinose family oligosaccharides inleaves of Ajuga reptens L.”, Plant Physiology 105:1335-1345, 1994) thatAjuga reptens plants (common bugle), a stachyose translocator from theunrelated Lamiaceae family also contains an alkaline α-galactosidase.This enzyme was partially characterized and found to have high affinityto stachyose. Also, leaves of the Peperomia camptotricha L. plant, fromthe family Piperaceae, show α-galactosidase activity at alkaline pH,suggesting that they also contain an alkaline α-galactosidase enzyme(Madore, M., “Catabolism of raffinose family oligosaccharides byvegetative sink tissues”, In: Carbon Partitioning and Source-SinkInteractions in Plants, Madore, M. and Lucas, W. J. (eds.) pp. 204-214,1995, American Society of Plant Physiologists, Maryland). Similarly, Gaoand Schaffer (Plant Physiol. 1999; 119:979-88, which is incorporatedfully herein by reference) have reported an α-galactosidase activitywith alkaline pH optimum in crude extracts of tissues from a variety ofspecies including members of the Cucurbit and Coleus (Lamiaceae)families.

Specific examples of plant alkaline α-galactosidase sequences areprovided in SEQ ID NOs: 4, 5 and 13 (Cucumis melo), 6 (T.tetragonioides), 7 and 12 (Cucumis sativus), 8 and 9 (Zea mays), 10(Oruza sativa), 11 (Pisum sativum) and 14 (Coffea arabica).

In some embodiments, the α-galactosidase is an acid α-galactosidase.

As used herein, “acid α-galactosidase” refers to α-galactosidasecharacterized by an ability to hydrolyse terminal-linked α-galactosemoieties from galactose-containing oligosaccharides under acidic pHconditions (e.g., about pH 4.2-5), such as occur in a lysosome.

The α-galactosidase of embodiments of the invention can be of any human,animal or plant source, provided no excessively adverse immunologicalreaction is induced upon in vivo administration (e.g., plant to human).

To reduce immunological reaction, a non-human α-galactosidasepreparation (e.g., of plant α-galactosidase) can be co-administered witha human α-galactosidase (i.e., acid human α-galactosidase).

Optionally, the multimeric protein structure further comprises at leastone mannose-6-phosphate (M6P) moiety. The M6P moiety (or moieties) maybe linked to one or more of the α-galactosidase monomers of themultimeric protein structure (e.g., via a linker).

Techniques and reagents for introducing M6P-containing moieties to abiomolecule (e.g., a polypeptide) are described in WO 2009/024977.

As exemplified in the Examples section herein, a multimeric proteinstructure described herein may be conveniently prepared by reactingα-galactosidase with a cross-linking agent.

Hence, according to another aspect of embodiments of the invention,there is provided a process of preparing a multimeric protein structuredescribed herein. The process comprises reacting α-galactosidase, so asto introduce at least one linking moiety which covalently links at leasttwo α-galactosidase monomers.

Optionally, the linking moiety is a bond (e.g., an amide bond, adisulfide bond) which links one α-galactosidase monomer to anotherα-galactosidase monomer. Optionally, the bond is introduced by usingsuitable conditions and/or reagents. For example, reagents which aresuitable for forming an amide bond from a carboxylic acid group and anamine group are known in the art.

Optionally, the linking moiety is a moiety which is not derived from apart of the α-galactosidase. For example, the linking moiety may be anoligomer, a polymer, a residue of a small molecule (e.g., an aminoacid).

In some embodiments, the linking moiety is introduced by reacting theα-galactosidase with a cross-linking agent which comprises the linkingmoiety (e.g., as described herein) and at least two reactive groups.

Optionally, the α-galactosidase is reacted under conditions in which thenative α-galactosidase is in a dimeric form.

In some embodiments, the cross-linking agent is reacted with theα-galactosidase at a molar ratio in a range of from 5:1 to 500:1(cross-linking agent: α-galactosidase monomer), optionally in a range offrom 50:1 to 400:1, and optionally in a range of from 75:1 to 300:1(e.g., about 100:1, about 200:1).

The process optionally further comprises purifying the cross-linkedprotein, for example, removing excess cross-linking agent. Commonpurification methods may be used, such as dialysis and/orultra-filtration using appropriate cut-off membranes and/or additionalchromatographic steps, including size exclusion chromatography, ionexchange chromatography, affinity chromatography, hydrophobicinteraction chromatography, and the like.

The reactive group is selected suitable for undergoing a chemicalreaction that leads to a bond formation with a complementaryfunctionality in the α-galactosidase monomer. Optionally, each reactivegroup is capable of forming a covalent bond between the linking moietydescribed herein and at least one polypeptide (e.g., so as to form afunctional group bound to the polypeptide, as described herein).

The reactive groups of a cross-linking agent may be identical to oneanother or different.

As used herein, the phrase “reactive group” describes a chemical groupthat is capable of undergoing a chemical reaction that typically leadsto a bond formation. The bond, according to the present embodiments, ispreferably a covalent bond (e.g., for each of the reactive groups).Chemical reactions that lead to a bond formation include, for example,nucleophilic and electrophilic substitutions, nucleophilic andelectrophilic addition reactions, alkylations, addition-eliminationreactions, cycloaddition reactions, rearrangement reactions and anyother known organic reactions that involve a functional group, as wellas combinations thereof.

The reactive group may optionally comprise a non-reactive portion (e.g.,an alkyl) which may serve, for example, to attach a reactive portion ofthe reactive group to a linking moiety (e.g., poly(alkylene glycol) oranalog thereof) described herein.

The reactive group is preferably selected so as to enable itsconjugation to α-galactosidase. Exemplary reactive groups include, butare not limited to, carboxylate (e.g., —CO₂H), thiol (—SH), amine(—NH₂), halo, azide (—N₃), isocyanate (—NCO), isothiocyanate (—N═C═S),hydroxy (—OH), carbonyl (e.g., aldehyde), maleimide, sulfate, phosphate,sulfonyl (e.g. mesyl, tosyl), etc. as well as activated groups, such asN-hydroxysuccinimide (NHS) (e.g. NHS esters),sulfo-N-hydroxysuccinimide, anhydride, acyl halide (—C(═O)-halogen) etc.

In some embodiments, the reactive group comprises a leaving group, suchas a leaving group susceptible to nucleophilic substitution (e.g., halo,sulfate, phosphate, carboxylate, N-hydroxysuccinimide).

Optionally, the reactive group may be in an activated form thereof.

As used herein, the phrase “activated form” describes a derivative of achemical group (e.g., a reactive group) which is more reactive than thechemical group, and which is thus readily capable of undergoing achemical reaction that leads to a bond formation. The activated form maycomprise a particularly suitable leaving group, thereby facilitatingsubstitution reactions. For example, a —C(═O)—NHS group(N-hydroxysuccinimide ester, or —C(═O)—O-succinimide) is a well-knownactivated form of —C(═O)OH, as NHS (N-hydroxysuccinimide) can be reactedwith a —C(═O)OH to form —C(═O)—NHS, which readily reacts to formproducts characteristic of reactions involving —C(═O)OH groups, such asamides and esters.

The reactive group can be attached to the rest of the linking moiety(e.g., a poly(alkylene glycol) or analog thereof) via different groups,atoms or bonds. These may include an ether bond [e.g., —O-alkyl-], anester bond [e.g., —O—C(═O)-alkyl-], a carbamate [e.g.,O—C(═O)—NH-alkyl-], etc. Thus, a variety of terminal groups can beemployed.

The following are non-limiting examples of the different groups that mayconstitute a reactive group as described herein: —CH₂CO₂H, —CH₂CH₂CO₂H,—CH₂CH₂SH, —CH₂CH₂NH₂, —CH₂CH₂N₃, —CH₂CH₂NCO, —CH₂—C(═O)—NHS,—CH₂CH₂—C(═O)—NHS, —C(═O)—CH₂—C(═O)—NHS,—CH₂CH₂—NHC(═O)CH₂CH₂-maleimide, etc.

The number of methylene groups in each of the above reactive groups ismerely exemplary, and may be varied.

The reactive group may also comprise the heteroatom at the end of apoly(alkylene glycol) chain (e.g., —OH).

In exemplary embodiments of the present invention, the reactive groupcomprises a carboxylate (e.g., an activated carboxylate such as anN-hydroxysuccinimide ester).

Optionally, the reactive group reacts with an amine group in theα-galactosidase (e.g., in a lysine residue and/or an N-terminus) to forman amide bond.

In some embodiments, the reaction of the reactive group comprisesreductive amination, wherein an amine group reacts with an aldehydegroup to form an imine, and the imine is reduced (e.g., by addition of areducing agent, such as sodium cyanoborohydride) to form an amine bond.The reactive group may be an amine group which reacts with an aldehydegroup of the α-galactosidase (e.g., on a saccharide moiety attached tothe polypeptide of the protein), or the reactive group may be analdehyde group which reacts with an amine group of the α-galactosidase(e.g., on a lysine residue). Optionally, a saccharide moiety ofα-galactosidase is oxidized by an oxidizing agent to form an aldehydegroup, prior to reaction of the reactive group with the α-galactosidase.For example, reaction of a saccharide with sodium periodate may be usedto produce a pair of aldehyde groups in a saccharide moiety.

In some embodiments, at least one of the reactive groups is selected soas to react with one functionality of an α-galactosidase monomer (e.g.,an amine group of a lysine residue or N-terminus), and at least one ofthe reactive groups is selected so as to react with a differentfunctionality of an α-galactosidase monomer (e.g., a thiol group of acysteine residue).

Optionally, one or more polypeptides described herein are reacted with aglycosylation reagent for introducing one or more M6P moieties, in orderto obtain an M6P-containing multimeric protein structure (e.g., asdescribed herein). Suitable M6P-containing glycosylation reagents andtheir use are described, for example, in WO 2009/024977.

As used herein, the terms “amine” and “amino” refer to either a —NR′R″group, wherein R′ and R″ are selected from the group consisting ofhydrogen, alkyl, cycloalkyl, heteroalicyclic (bonded through a ringcarbon), aryl and heteroaryl (bonded through a ring carbon). R′ and R″are bound via a carbon atom thereof. Optionally, R′ and R″ are selectedfrom the group consisting of hydrogen and alkyl comprising 1 to 4 carbonatoms. Optionally, R′ and R″ are hydrogen.

As used herein throughout, the term “alkyl” refers to a saturatedaliphatic hydrocarbon including straight chain and branched chaingroups. Preferably, the alkyl group has 1 to 20 carbon atoms. Whenever anumerical range; e.g., “1-20”, is stated herein, it implies that thegroup, in this case the alkyl group, may contain 1 carbon atom, 2 carbonatoms, 3 carbon atoms, etc., up to and including 20 carbon atoms. Morepreferably, the alkyl is a medium size alkyl having 1 to 10 carbonatoms. Most preferably, unless otherwise indicated, the alkyl is a loweralkyl having 1 to 4 carbon atoms. The alkyl group may be substituted orunsubstituted. When substituted, the substituent group can be, forexample, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl,heteroalicyclic, halo, hydroxy, alkoxy, aryloxy, thiohydroxy,thioalkoxy, thioaryloxy, sulfinyl, sulfonyl, cyano, nitro, azide,phosphonyl, phosphinyl, oxo, carbonyl, thiocarbonyl, urea, thiourea,O-carbamyl, N-carbamyl, O-thiocarbamyl, N-thiocarbamyl, C-amido,N-amido, C-carboxy, O-carboxy, sulfonamido, and amino, as these termsare defined herein.

A “cycloalkyl” group refers to an all-carbon monocyclic or fused ring(i.e., rings which share an adjacent pair of carbon atoms) group whereinone of more of the rings does not have a completely conjugatedpi-electron system. Examples, without limitation, of cycloalkyl groupsare cyclopropane, cyclobutane, cyclopentane, cyclopentene, cyclohexane,cyclohexadiene, cycloheptane, cycloheptatriene, and adamantane. Acycloalkyl group may be substituted or unsubstituted. When substituted,the substituent group can be, for example, alkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, halo, hydroxy, alkoxy, aryloxy,thiohydroxy, thioalkoxy, thioaryloxy, sulfinyl, sulfonyl, cyano, nitro,azide, phosphonyl, phosphinyl, oxo, carbonyl, thiocarbonyl, urea,thiourea, O-carbamyl, N-carbamyl, O-thiocarbamyl, N-thiocarbamyl,C-amido, N-amido, C-carboxy, O-carboxy, sulfonamido, and amino, as theseterms are defined herein.

An “alkenyl” group refers to an alkyl group which consists of at leasttwo carbon atoms and at least one carbon-carbon double bond.

An “alkynyl” group refers to an alkyl group which consists of at leasttwo carbon atoms and at least one carbon-carbon triple bond.

An “aryl” group refers to an all-carbon monocyclic or fused-ringpolycyclic (i.e., rings which share adjacent pairs of carbon atoms)groups having a completely conjugated pi-electron system. Examples,without limitation, of aryl groups are phenyl, naphthalenyl andanthracenyl. The aryl group may be substituted or unsubstituted. Whensubstituted, the substituent group can be, for example, alkyl, alkenyl,alkynyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, halo, hydroxy,alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, sulfinyl,sulfonyl, cyano, nitro, azide, phosphonyl, phosphinyl, oxo, carbonyl,thiocarbonyl, urea, thiourea, O-carbamyl, N-carbamyl, O-thiocarbamyl,N-thiocarbamyl, C-amido, N-amido, C-carboxy, O-carboxy, sulfonamido, andamino, as these terms are defined herein.

A “heteroaryl” group refers to a monocyclic or fused ring (i.e., ringswhich share an adjacent pair of atoms) group having in the ring(s) oneor more atoms, such as, for example, nitrogen, oxygen and sulfur and, inaddition, having a completely conjugated pi-electron system. Examples,without limitation, of heteroaryl groups include pyrrole, furane,thiophene, imidazole, oxazole, thiazole, pyrazole, pyridine, pyrimidine,quinoline, isoquinoline and purine. The heteroaryl group may besubstituted or unsubstituted. When substituted, the substituent groupcan be, for example, alkyl, alkenyl, alkynyl, cycloalkyl, aryl,heteroaryl, heteroalicyclic, halo, hydroxy, alkoxy, aryloxy,thiohydroxy, thioalkoxy, thioaryloxy, sulfinyl, sulfonyl, cyano, nitro,azide, phosphonyl, phosphinyl, oxo, carbonyl, thiocarbonyl, urea,thiourea, O-carbamyl, N-carbamyl, O-thiocarbamyl, N-thiocarbamyl,C-amido, N-amido, C-carboxy, O-carboxy, sulfonamido, and amino, as theseterms are defined herein.

A “heteroalicyclic” group refers to a monocyclic or fused ring grouphaving in the ring(s) one or more atoms such as nitrogen, oxygen andsulfur. The rings may also have one or more double bonds. However, therings do not have a completely conjugated pi-electron system. Theheteroalicyclic may be substituted or unsubstituted. When substituted,the substituted group can be, for example, lone pair electrons, alkyl,alkenyl, alkynyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, halo,hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy,sulfinyl, sulfonyl, cyano, nitro, azide, phosphonyl, phosphinyl, oxo,carbonyl, thiocarbonyl, urea, thiourea, O-carbamyl, N-carbamyl,O-thiocarbamyl, N-thiocarbamyl, C-amido, N-amido, C-carboxy, O-carboxy,sulfonamido, and amino, as these terms are defined herein.Representative examples are piperidine, piperazine, tetrahydrofuran,tetrahydropyran, morpholine and the like.

A “hydroxy” group refers to an —OH group.

An “azide” group refers to a —N═N⁺═N⁻ group.

An “alkoxy” group refers to both an —O-alkyl and an —O-cycloalkyl group,as defined herein.

An “aryloxy” group refers to both an —O-aryl and an —O-heteroaryl group,as defined herein.

An “ether” refers to both an alkoxy and an aryloxy group, wherein thegroup is linked to an alkyl, alkenyl, alkynyl, cycloalkyl, aryl,heteroaryl or heteroalicyclic group.

An ether bond describes a —O— bond.

A “thiohydroxy” or “thiol” group refers to a —SH group.

A “thioalkoxy” group refers to both an —S-alkyl group, and an—S-cycloalkyl group, as defined herein.

A “thioaryloxy” group refers to both an —S-aryl and an —S-heteroarylgroup, as defined herein.

A “thioether” refers to both a thioalkoxy and a thioaryloxy group,wherein the group is linked to an alkyl, alkenyl, alkynyl, cycloalkyl,aryl, heteroaryl or heteroalicyclic group.

A thioether bond describes a —S— bond.

A “disulfide” group refers to both a —S-thioalkoxy and a —S-thioaryloxygroup.

A disulfide bond describes a —S—S— bond.

A “carbonyl” group refers to a —C(═O)—R′ group, where R′ is defined ashereinabove.

A “thiocarbonyl” group refers to a —C(═S)—R′ group, where R′ is asdefined herein.

A “carboxyl” refers to both “C-carboxy” and O-carboxy”.

A “C-carboxy” group refers to a —C(═O)—O—R′ groups, where R′ is asdefined herein.

An “O-carboxy” group refers to an R′C(═O)—O— group, where R′ is asdefined herein.

An “oxo” group refers to a ═O group.

A “carboxylate” or “carboxyl” encompasses both C-carboxy and O-carboxygroups, as defined herein.

A “carboxylic acid” group refers to a C-carboxy group in which R′ ishydrogen.

A “thiocarboxy” or “thiocarboxylate” group refers to both —C(═S)—O—R′and —O—C(═S)R′ groups.

An “ester” refers to a C-carboxy group wherein R′ is not hydrogen.

An ester bond refers to a —O—C(═O)— bond.

A thioester bond refers to a —O—C(═S)— bond or to a —S—C(═O) bond.

A “halo” group refers to fluorine, chlorine, bromine or iodine.

A “sulfinyl” group refers to an —S(═O)—R′ group, where R′ is as definedherein.

A “sulfonyl” group refers to an —S(═O)₂—R′ group, where R′ is as definedherein.

A “sulfonate” group refers to an —S(═O)₂—O—R′ group, where R′ is asdefined herein.

A “sulfate” group refers to an —O—S(═O)₂—O—R′ group, where R′ is asdefined as herein.

A “sulfonamide” or “sulfonamido” group encompasses both S-sulfonamidoand N-sulfonamido groups, as defined herein.

An “S-sulfonamido” group refers to a —S(═O)₂—NR′R″ group, with each ofR′ and R″ as defined herein.

An “N-sulfonamido” group refers to an R'S(═O)₂—NR″ group, where each ofR′ and R″ is as defined herein.

An “O-carbamyl” group refers to an —OC(═O)—NR′R″ group, where each of R′and R″ is as defined herein.

An “N-carbamyl” group refers to an R′OC(═O)—NR″— group, where each of R′and R″ is as defined herein.

A “carbamyl” or “carbamate” group encompasses O-carbamyl and N-carbamylgroups.

A carbamate bond describes a —O—C(═O)—NR′— bond, where R′ is asdescribed herein.

An “O-thiocarbamyl” group refers to an —OC(═S)—NR′R″ group, where eachof R′ and R″ is as defined herein.

An “N-thiocarbamyl” group refers to an R′OC(═S)NR″— group, where each ofR′ and R″ is as defined herein.

A “thiocarbamyl” or “thiocarbamate” group encompasses O-thiocarbamyl andN-thiocarbamyl groups.

A thiocarbamate bond describes a —O—C(═S)—NR′— bond, where R′ is asdescribed herein.

A “C-amido” group refers to a —C(═O)—NR′R″ group, where each of R′ andR″ is as defined herein.

An “N-amido” group refers to an R′C(═O)—NR″— group, where each of R′ andR″ is as defined herein.

An “amide” group encompasses both C-amido and N-amido groups.

An amide bond describes a —NR′—C(═O)— bond, where R′ is as definedherein.

An amine bond describes a bond between a nitrogen atom in an amine group(as defined herein) and an R′ group in the amine group.

A thioamide bond describes a —NR′—C(═S)— bond, where R′ is as definedherein.

A “urea” group refers to an —N(R′)—C(═O)—NR″R′″ group, where each of R′and R″ is as defined herein, and R′″ is defined as R′ and R″ are definedherein.

A “nitro” group refers to an —NO₂ group.

A “cyano” group refers to a —C≡N group.

The term “phosphonyl” or “phosphonate” describes a —P(═O)(OR′) (OR″)group, with R′ and R″ as defined hereinabove.

The term “phosphate” describes an —O—P(═O)(OR′) (OR″) group, with eachof R′ and R″ as defined hereinabove.

A “phosphoric acid” is a phosphate group is which each of R is hydrogen.

The term “phosphinyl” describes a —PR′R″ group, with each of R′ and R″as defined hereinabove.

The term “thiourea” describes a —N(R′)—C(═S)—NR″— group, with each of R′and R″ as defined hereinabove.

As described herein, multimeric protein structures described herein mayexhibit improved stability and stronger and/or longer lastingα-galactosidase activity at therapeutically important sites in vivo.Such multimeric protein structures are therefore highly beneficial foruse in various medical applications in which α-galactosidase activity isdesirable, including therapeutic and research applications.

Hence, according to some embodiments, the multimeric protein structuredescribed herein is for use as a medicament, for example, a medicamentfor treating Fabry disease.

According to another aspect of embodiments of the invention, there isprovided a method of treating Fabry disease, the method comprisingadministering to a subject in need thereof a therapeutically effectiveamount of a multimeric protein structure described herein.

According to another aspect of embodiments of the invention, there isprovided a pharmaceutical composition that comprises a multimericprotein structure as described herein and a pharmaceutically acceptablecarrier.

As used herein a “pharmaceutical composition” refers to a preparation ofone or more of the multimeric protein structures described herein, withother chemical components such as pharmaceutically acceptable andsuitable carriers and excipients. The purpose of a pharmaceuticalcomposition is to facilitate administration of a compound to anorganism.

Hereinafter, the term “pharmaceutically acceptable carrier” refers to acarrier or a diluent that does not cause significant irritation to anorganism and does not abrogate the biological activity and properties ofthe administered compound. Examples, without limitations, of carriersare: propylene glycol, saline, emulsions and mixtures of organicsolvents with water, as well as solid (e.g., powdered) and gaseouscarriers.

Herein the term “excipient” refers to an inert substance added to apharmaceutical composition to further facilitate administration of acompound. Examples, without limitation, of excipients include calciumcarbonate, calcium phosphate, various sugars and types of starch,cellulose derivatives, gelatin, vegetable oils and polyethylene glycols.

The pharmaceutical composition optionally comprises an additionalingredient which further stabilizes the α-galactosidase of themultimeric protein structure. Optionally, the additional ingredient isgalactose.

Alternatively, a galactose derivative (e.g., a galactose-containingglycoside) may be used instead of galactose. Optionally, a non-reducinggalactose derivative is used.

Techniques for formulation and administration of drugs may be found in“Remington's Pharmaceutical Sciences” Mack Publishing Co., Easton, Pa.,latest edition, which is incorporated herein by reference.

Pharmaceutical compositions of the present invention may be manufacturedby processes well known in the art, e.g., by means of conventionalmixing, dissolving, granulating, dragee-making, levigating, emulsifying,encapsulating, entrapping or lyophilizing processes.

Pharmaceutical compositions for use in accordance with the presentinvention thus may be formulated in conventional manner using one ormore pharmaceutically acceptable carriers comprising excipients andauxiliaries, which facilitate processing of the multimeric proteinstructure into preparations which can be used pharmaceutically. Properformulation is dependent upon the route of administration chosen.

For injection or infusion, the multimeric protein structures ofembodiments of the invention may be formulated in aqueous solutions,preferably in physiologically compatible buffers such as Hank'ssolution, Ringer's solution, or physiological saline buffer with orwithout organic solvents such as propylene glycol, polyethylene glycol.

For transmucosal administration, penetrants are used in the formulation.Such penetrants are generally known in the art.

For oral administration, the multimeric protein structures of theinvention can be formulated readily by combining the multimeric proteinstructures with pharmaceutically acceptable carriers well known in theart. Such carriers enable the multimeric protein structures describedherein to be formulated as tablets, pills, dragees, capsules, liquids,gels, syrups, slurries, suspensions, and the like, for oral ingestion bya patient. Pharmacological preparations for oral use can be made using asolid excipient, optionally grinding the resulting mixture, andprocessing the mixture of granules, after adding suitable auxiliaries ifdesired, to obtain tablets or dragee cores. Suitable excipients are, inparticular, fillers such as sugars, including lactose, sucrose,mannitol, or sorbitol; cellulose preparations such as, for example,maize starch, wheat starch, rice starch, potato starch, gelatin, gumtragacanth, methyl cellulose, hydroxypropylmethyl-cellulose, sodiumcarbomethylcellulose; and/or physiologically acceptable polymers such aspolyvinylpyrrolidone (PVP). If desired, disintegrating agents may beadded, such as cross-linked polyvinyl pyrrolidone, agar, or alginic acidor a salt thereof such as sodium alginate.

Dragee cores are provided with suitable coatings. For this purpose,concentrated sugar solutions may be used which may optionally containgum arabic, talc, polyvinyl pyrrolidone, carbopol gel, polyethyleneglycol, titanium dioxide, lacquer solutions and suitable organicsolvents or solvent mixtures. Dyestuffs or pigments may be added to thetablets or dragee coatings for identification or to characterizedifferent combinations of doses of active multimeric protein structure.

Pharmaceutical compositions, which can be used orally, include push-fitcapsules made of gelatin as well as soft, sealed capsules made ofgelatin and a plasticizer, such as glycerol or sorbitol. The push-fitcapsules may contain the active ingredients in admixture with fillersuch as lactose, binders such as starches, lubricants such as talc ormagnesium stearate and, optionally, stabilizers. In soft capsules, themultimeric protein structures may be dissolved or suspended in suitableliquids, such as fatty oils, liquid paraffin, or liquid polyethyleneglycols. In addition, stabilizers may be added. All formulations fororal administration should be in dosages suitable for the chosen routeof administration.

For buccal administration, the compositions may take the form of tabletsor lozenges formulated in conventional manner.

For administration by inhalation, the multimeric protein structures foruse according to embodiments of the present invention are convenientlydelivered in the form of an aerosol spray presentation (which typicallyincludes powdered, liquified and/or gaseous carriers) from a pressurizedpack or a nebulizer, with the use of a suitable propellant, e.g.,dichlorodifluoromethane, trichlorofluoromethane,dichloro-tetrafluoroethane or carbon dioxide. In the case of apressurized aerosol, the dosage unit may be determined by providing avalve to deliver a metered amount. Capsules and cartridges of, e.g.,gelatin for use in an inhaler or insufflator may be formulatedcontaining a powder mix of the multimeric protein structures and asuitable powder base such as, but not limited to, lactose or starch.

The multimeric protein structures described herein may be formulated forparenteral administration, e.g., by bolus injection or continuousinfusion. Formulations for injection or infusion may be presented inunit dosage form, e.g., in ampoules or in multidose containers withoptionally, an added preservative. The compositions may be suspensions,solutions or emulsions in oily or aqueous vehicles, and may containformulatory agents such as suspending, stabilizing and/or dispersingagents.

Pharmaceutical compositions for parenteral administration includeaqueous solutions of the multimeric protein structure preparation inwater-soluble form. Additionally, suspensions of the multimeric proteinstructures may be prepared as appropriate oily injection suspensions andemulsions (e.g., water-in-oil, oil-in-water or water-in-oil in oilemulsions). Suitable lipophilic solvents or vehicles include fatty oilssuch as sesame oil, or synthetic fatty acids esters such as ethyloleate, triglycerides or liposomes. Aqueous injection suspensions maycontain substances, which increase the viscosity of the suspension, suchas sodium carboxymethyl cellulose, sorbitol or dextran. Optionally, thesuspension may also contain suitable stabilizers or agents, whichincrease the solubility of the multimeric protein structures to allowfor the preparation of highly concentrated solutions.

Alternatively, the multimeric protein structures may be in powder formfor constitution with a suitable vehicle, e.g., sterile, pyrogen-freewater, before use.

The multimeric protein structure of embodiments of the present inventionmay also be formulated in rectal compositions such as suppositories orretention enemas, using, e.g., conventional suppository bases such ascocoa butter or other glycerides.

The pharmaceutical compositions herein described may also comprisesuitable solid of gel phase carriers or excipients. Examples of suchcarriers or excipients include, but are not limited to, calciumcarbonate, calcium phosphate, various sugars, starches, cellulosederivatives, gelatin and polymers such as polyethylene glycols.

Pharmaceutical compositions suitable for use in the context of thepresent invention include compositions wherein the active ingredientsare contained in an amount effective to achieve the intended purpose.More specifically, a therapeutically effective amount means an amount ofmultimeric protein structures effective to prevent, alleviate orameliorate symptoms of disease or prolong the survival of the subjectbeing treated.

For any multimeric protein structures used in the methods of theinvention, the therapeutically effective amount or dose can be estimatedinitially from activity assays in animals. For example, a dose can beformulated in animal models to achieve a circulating concentration rangethat includes the IC₅₀ as determined by activity assays (e.g., theconcentration of the test protein structures, which achieves ahalf-maximal increase in a biological activity of the multimeric proteinstructure). Such information can be used to more accurately determineuseful doses in humans.

As is demonstrated in the Examples section that follows, atherapeutically effective amount for the multimeric protein structuresof embodiments of the present invention may range between about 1 μg/kgbody weight and about 500 mg/kg body weight.

Toxicity and therapeutic efficacy of the multimeric protein structuresdescribed herein can be determined by standard pharmaceutical proceduresin experimental animals, e.g., by determining the EC₅₀, the IC₅₀ and theLD₅₀ (lethal dose causing death in 50% of the tested animals) for asubject protein structure. The data obtained from these activity assaysand animal studies can be used in formulating a range of dosage for usein human.

The dosage may vary depending upon the dosage form employed and theroute of administration utilized. The exact formulation, route ofadministration and dosage can be chosen by the individual physician inview of the patient's condition. (See e.g., Fingl et al., 1975, in “ThePharmacological Basis of Therapeutics”, Ch. 1 p.1).

Dosage amount and interval may be adjusted individually to provideplasma levels of the active moiety which are sufficient to maintain thedesired effects, termed the minimal effective concentration (MEC). TheMEC will vary for each preparation, but can be estimated from in vitrodata; e.g., the concentration necessary to achieve the desired level ofactivity in vitro. Dosages necessary to achieve the MEC will depend onindividual characteristics and route of administration. HPLC assays orbioassays can be used to determine plasma concentrations.

Dosage intervals can also be determined using the MEC value.Preparations should be administered using a regimen, which maintainsplasma levels above the MEC for 10-90% of the time, preferable between30-90% and most preferably 50-90%.

Depending on the severity and responsiveness of the condition to betreated, dosing can also be a single administration of a slow releasecomposition described hereinabove, with course of treatment lasting fromseveral days to several weeks or until cure is effected or diminution ofthe disease state is achieved.

The amount of a composition to be administered will, of course, bedependent on the subject being treated, the severity of the affliction,the manner of administration, the judgment of the prescribing physician,etc.

Compositions of the present invention may, if desired, be presented in apack or dispenser device, such as an FDA (the U.S. Food and DrugAdministration) approved kit, which may contain one or more unit dosageforms containing the active ingredient. The pack may, for example,comprise metal or plastic foil, such as, but not limited to a blisterpack or a pressurized container (for inhalation). The pack or dispenserdevice may be accompanied by instructions for administration. The packor dispenser may also be accompanied by a notice associated with thecontainer in a form prescribed by a governmental agency regulating themanufacture, use or sale of pharmaceuticals, which notice is reflectiveof approval by the agency of the form of the compositions for human orveterinary administration. Such notice, for example, may be of labelingapproved by the U.S. Food and Drug Administration for prescription drugsor of an approved product insert. Compositions comprising a multimericprotein structure of embodiments of the invention formulated in acompatible pharmaceutical carrier may also be prepared, placed in anappropriate container, and labeled for treatment of an indicatedcondition or diagnosis, as is detailed herein.

Thus, according to an embodiment of the present invention, depending onthe selected multimeric protein structures, the pharmaceuticalcomposition described herein is packaged in a packaging material andidentified in print, in or on the packaging material, for use in thetreatment of a condition in which the activity of the multimeric proteinstructure is beneficial, as described hereinabove.

As used herein the term “about” refers to ±10%

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of means “including and limited to”.

The word “exemplary” is used herein to mean “serving as an example,instance or illustration”. Any embodiment described as “exemplary” isnot necessarily to be construed as preferred or advantageous over otherembodiments and/or to exclude the incorporation of features from otherembodiments.

The word “optionally” is used herein to mean “is provided in someembodiments and not provided in other embodiments”. Any particularembodiment of the invention may include a plurality of “optional”features unless such features conflict.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention maybe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

As used herein the term “method” refers to manners, means, techniquesand procedures for accomplishing a given task including, but not limitedto, those manners, means, techniques and procedures either known to, orreadily developed from known manners, means, techniques and proceduresby practitioners of the chemical, pharmacological, biological,biochemical and medical arts.

As used herein, the term “treating” includes abrogating, substantiallyinhibiting, slowing or reversing the progression of a condition,substantially ameliorating clinical or aesthetical symptoms of acondition or substantially preventing the appearance of clinical oraesthetical symptoms of a condition.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Various embodiments and aspects of the present invention as delineatedhereinabove and as claimed in the claims section below find experimentalsupport in the following examples.

EXAMPLES

Reference is now made to the following examples, which together with theabove descriptions illustrate some embodiments of the invention in a nonlimiting fashion.

Materials and Methods

Materials:

bis-N-hydroxysuccinimide-poly(ethylene glycol) (bis-NHS-PEG) wasobtained from Iris Biotech GmbH in PEG₈ and 2000 Dalton (PEG₄₅) PEGforms, and from Pierce in PEG₅ form, and dissolved in dimethyl sulfoxide(DMSO) at a concentration of 25 mg/mL;

Citric acid was obtained from Sigma;

Coomassie Blue G250 was obtained from Bio-Rad;

Dimethyl sulfoxide was obtained from Sigma;

D-(+)-galactose was obtained from Sigma;

Human plasma (K3 EDTA) was obtained from Bioreclamation Inc.;

4-Methylumbelliferone was obtained from Sigma;

4-Methylumbelliferyl-α-D-galactopyranoside was obtained from Sigma;

N-dodecanoyl-nitrobenzoxadiazole-ceramide trihexoside (Gb₃-NBD) wasobtained from Matreya;

2-(N-morpholino)ethanesulfonic acid was obtained from Merck;

Phosphate buffered saline was obtained from Sigma;

p-Nitrophenyl-α-D-galactopyranoside was obtained from Sigma;

Primuline was obtained from Sigma; Primuline spray reagent was preparedby dissolving 12.5 mg primuline in 200 ml acetone:water (8:2 volumeratio);

Pyridine was obtained from Sigma;

Sinapinic acid was obtained from Sigma;

Sodium carbonate was obtained from Sigma;

Sodium phosphate was obtained from Sigma;

Sodium taurocholate was obtained from Sigma;

Trifluoroacetic acid was obtained from Sigma.

Plant Recombinant Human α-GAL-I:

Plant recombinant human α-GAL (prh-α-GAL) having SEQ ID NO: 1, referredto herein as plant recombinant human α-GAL-I (prh-α-GAL-I), was preparedas described in International Patent Application PCT/IL2008/000576(published as WO 2008/132743).

Transgenic plant material was generated using Nicotiana Benthamianaplants infiltrated with genetic construct containing the expressioncassette for α-GAL-A, for expressing the human α-GAL-A protein. This wasperformed in a growth chamber under controlled conditions. This wasfollowed by harvest of plant material and extraction of soluble proteinsfrom the plant cells. prh-α-GAL-A was then purified by a purificationprocess involving standard methods for protein purification followed bya chemical modification step to manufacture the cross-linked protein.The current prh-α-GAL-A was extracted from plant material usinghomogenizers. The plant debris was removed by centrifugation and theprotein was further purified using ammonium sulfate precipitation andacidification steps. The supernatant was filtered and loaded onto ahydrophobic column, followed by desalting and loading onto a cationexchange column. The pool of the cation exchange column wasconcentrated.

Plant Recombinant Human α-GAL-II:

Plant recombinant human α-GAL comprising a mixture of α-GAL having SEQID NO: 2 and α-GAL having SEQ ID NO: 3 (without the N-terminal aminoacids EF present in SEQ ID NO: 1), referred to herein as prh-α-GAL-II,was prepared by a process similar to that described above forprh-α-GAL-I, using a different genetic construct.

cDNA encoding the human α-galactosidase protein (EC 3.2.1-22 GenBank:X05790) was optimized and synthesized by GENEART AG (Regensburg,Germany). The codon usage without the leader peptide (endoplasmicreticulum target signal peptide) was adapted to the codon bias ofNicotiana tobaccum genes. During the optimization process the followingcis-acting sequence motifs were avoided: internal TATA-boxes, chi-sitesand ribosomal entry sites, AT-rich or GC-rich sequence stretches, RNAinstability elements (“killer motifs”), repeat sequences and RNAsecondary structures, splice donor (cryptic) and acceptor sites, branchpoints. In addition, regions of very high (>80%) or very low (<30%) GCcontent has been avoided.

The nucleotide sequence of the native human α-galactosidase leaderpeptide (endoplasmic reticulum target signal peptide) of full lengthhuman α-galactosidase protein (GenBank: X05790) was replaced with anucleotide sequence encoding the 33 amino acid endoplasmic reticulumtargeting signal peptide (leader peptide) of the Arabidopsis ABPIprotein. This signal peptide provides efficient targeting ofα-galactosidase to the secretory pathway and is cleaved from thepolypeptide, by signal peptidase, once the protein has been translocatedinto the endoplasmic reticulum. A nucleotide sequence encoding theendoplasmic reticulum retention signal SEKDEL was added to the cDNAsequence at the 3′ terminus, allowing retrieval of the expressed proteinfrom the Golgi apparatus, effectively maintaining the protein in theendoplasmic reticulum.

The protein of interest was expressed from a strong subgenomic viralpromoter of the coat protein. The system relies on transientamplification (by agroinfection) of viral vectors delivered to a plantby Agrobacterium. In agroinfection, a plant functional promoter and thecDNA encoding a viral replicon are transferred as T-DNA fromAgrobacterium into plant cells. The T-DNA is transcribed in-planta bythe plant promoter to generate biologically active viral RNA thatinitiates self replication.

For the transient expression a 3 vector recombination system based onthe system previously developed as described [Gleba et al., Vaccine2005, 23:2042-2048]. One of the vectors was inserted withα-galactosidase cDNA and the two other vectors containing genes forconstruction of the whole viral replicon (RdRp and Integrase), thusgenerating the biologically active viral RNA that can initiate selfreplication

N. Benthamiana plants were germinated and grown in commercial mix soil(Givaat Ada, IL) supplemented with granular slow release fertilizer(Scott Marysville, Ohio) under a long day (16 hours light/8 hours dark)light regime at 24-25° C.

Agrobacteria were transformed with the pICH20866-alpha-GAL basedreplicon vector system using electroporation (2500 V, 5 milliseconds)[den Dulk-Ra and Hooykaas, Methods Mol Biol 1995, 55:63-72]. Plants wereinfiltrated with Agrobacteria containing the 3 ICON plasmids by vacuuminfiltration with standard methods known in the art. Briefly, N.benthamiana plants, 5-6 week old, were infiltrated by immersing allaerial plant organs into a bacterial suspension and were placed in avacuum chamber. A minus (−) 0.8 bar vacuum was applied for 1 minute,followed by a quick return to atmospheric pressure. Plants were returnedto the greenhouse for additional 5-7 days under the same growthconditions.

Samples of Nicotiana benthamiana leaves were harvested 5 days postinfiltration and extracted in Laemmli buffer for SDS-PAGE, or inactivity assay buffer (20 mM citric acid, 30 mM sodium phosphate, 0.1%bovine serum albumin and 0.67% ethanol, pH 4.6.) for assay of catalyticactivity of the plant expressed protein.

Human α-galactosidase protein from plant extracts was purified by atwo-step ammonium sulfate differential precipitation (“salting out”:1^(st) step 0.57 M; 2^(nd) step 2.27 M), followed by hydrophobicinteraction chromatography (Phenyl 650 M resin) and cation exchangechromatography.

Two sequences (i.e., SEQ ID NO: 2 and SEQ ID NO: 3), which differ in thepresence or absence of an N-terminal glycine, were obtained due todifferent leader sequence processing.

4-Methylumbelliferyl-α-D-galactopyranoside assay of α-GAL activity:

α-GAL activity was measured using4-methylumbelliferyl-α-D-galactopyranoside as a hydrolysis substrate.The assay was performed in citrate-phosphate buffer (20 mM citric acid,30 mM sodium phosphate, pH 4.6). 10 μL of sample containing the testedα-GAL was incubated with 40 μL assay buffer containing 5 mM4-methylumbelliferyl-α-D-galactopyranoside. The reaction mixture wasincubated at 37° C. for 60 minutes. 10 μL of the reaction mixture weretransferred into a black 96-well plate (Greiner), 90 μL of stop solution(2 M sodium carbonate) was added, and fluorescence was measured at anexcitation wavelength of 365 nm and an emission wavelength of 450 nm.Fluorescence was translated to product concentration, and further toactivity, using a calibration curve of 4-methylumbelliferone, thereaction product.

N-Dodecanoyl-nitrobenzoxadiazole-ceramide trihexoside (Gb₃-NBD) assay ofα-GAL activity

The fluorescently labeled substrateN-dodecanoyl-nitrobenzoxadiazole-ceramide trihexoside (Gb₃-NBD) is lesslipophilic than Gb₃, facilitating its use in in-vitro enzymaticreactions.

10 μL of 0.1 μg/μL Gb₃-NBD (in water with 10% ethanol), and 5 μL of 0.2mg/mL α-GAL were added to 85 μL of citrate-phosphate buffer at a pH of4.6. The final α-GAL concentration was 10 μg/mL. The background ornon-catalyzed reaction, without α-GAL, was composed of 90 μL ofcitrate-phosphate buffer at a pH of 4.6 with 10 μL of 0.1 μg/μL Gb₃-NBD(in water with 10% ethanol). The reaction mixtures were incubated for 60minutes at 37° C. Following the incubation, 50 μL methanol was added tothe reaction mixture, and the solutions were vortexed for 1 minute. 100μL chloroform was then added, and the solutions were further vortexedfor 1 minute. Water and organic solvents were removed under vacuum usinga Speed Vac system. The residues were dissolved in 80 μL ofchloroform:methanol (1:1). 30 μL of each sample was loaded on HPTLC(high performance thin layer chromatography) Silica Gel 60 plates(Merck) using a Linomat V system (CAMAG). HPTLC plates were developedusing a chloroform:methanol:H₂O solution at a ratio of 100:42:6 as asolvent system. Plates were then allowed to dry and the substrate andproduct spots were visualized by irradiation under UV light at awavelength of 365 nm.

p-Nitrophenyl-α-D-galactopyranoside (p-NP-G) assay of α-GAL activity:

p-Nitrophenyl-α-D-galactopyranoside was used as a hydrolysis substratefor α-GAL activity assays. The assay buffer contained 20 mM citric acid,30 mM sodium phosphate, 0.1% BSA (bovine serum albumin) and 0.67%ethanol at pH 4.6. The assay was performed in 96 well ELISA plates(Greiner). 50 μL of sample were incubated with 150 μL assay buffer and30 μL substrate was added to obtain a final concentration of 8 mMp-nitrophenyl-α-D-galactopyranoside. The reaction mixture was incubatedat 37° C. for 90 minutes. After 90 minutes, 100 μL of 1.98 M sodiumcarbonate was added to each well in order to terminate the reaction. Theamount of reaction product was determined by measuring absorbance at 405nm.

Measurement of α-GAL Stability In Vitro:

The stability of α-GAL from various sources was determined by addingα-GAL to one of the following conditions:

1) simulated lysosomal conditions: citrate-phosphate buffer (20 mMcitric acid, 30 mM sodium phosphate), pH 4.6, 37° C.;

2) simulated physiological conditions: phosphate buffered saline (PBS),pH 7.4, 37° C.;

3) human plasma at 37° C.

The α-GAL was added at a concentration of 1 μg/mL, as determined by theactivity of α-GAL in the solution, and the solution was incubated at 37°C. Samples of each solution were withdrawn at predetermined time pointsand the α-GAL activity was measured as described hereinabove. The valueof the enzymatic activity immediately after addition of the tested α-GALto each environment was defined as 100%, and further activity results atthe tested time points were calculated as a percentage of that initialactivity.

Pharmacokinetics of α-GAL:

Individual Fabry (α-Gal-A −/0) mice were placed in an illuminatedplexiglass restraining device, and the enzyme was injected into the tailvein. Blood samples were obtained at the indicated times after injectionby either tail bleed or retro-orbital eye bleed, using heparinizedmicrohematocrit tubes. Plasma was diluted in4-methylumbelliferyl-α-D-galactopyranoside activity buffer. A4-methylumbelliferyl-α-D-galactopyranoside assay was performed asdescribed above.

Terminal elimination half-life (T_(1/2)) was calculated based on plasmaactivity results. The terminal half-life (elimination half-life) is thetime required for the plasma concentration to decrease by 50% afterpseudo-equilibrium of distribution has been reached. The terminalhalf-life was calculated from the terminal (log-linear) portion of thecurve, by linear regression of time vs. log concentration [Toutain &Bousquet-Melou, J Vet Pharmacol Ther 2004, 27:427-39].

Bio-Distribution of α-GAL:

Fabry (α-Gal-A −/0) mice were injected intravenously (in the tail vein)with α-GAL at a dose of 2 mg/Kg. Tissues (livers, kidneys, hearts, andspleens) were harvested 2 hours, 24 hours, 3 days, 7 days, 14 days or 28days post-injection of the enzyme. α-GAL levels in normal control miceand in saline-administered (untreated) Fabry mice were compared with thelevels in Fabry mice that received exogenous α-GAL. To determine theα-GAL activity in tissues, thawed tissue samples were placed in 2 mLpolypropylene tubes containing lysis buffer (28 mM citric acid, 44 mMdibasic sodium phosphate, 0.5% sodium taurocholate, pH 4.4) as describedin Oshima et al. [PNAS 1997, 94:2540-2544]. The samples were homogenizedby use of a Tissuelyzer (Retsch MM400) for 10 minutes. Debris waspelleted by centrifugation at 4° C., and the resulting supernatants wereassayed for α-GAL activity by a4-methylumbelliferyl-α-D-galactopyranoside assay, as described above.The same samples were also subjected to Western blot analysis.

In Vivo Gb₃ Assay:

The end point efficacy of injected α-GAL was measured by assay of Gb₃levels of the animal tissues, in order to determine whether Gb₃ levelswere decreased by α-GAL activity.

To measure Gb₃ hydrolysis, neutral glycosphingolipids were extractedfrom target organs (e.g., liver, kidney, heart and spleen). 100 mgtissue samples were homogenized in 1 mL of 2:1 (v/v) chloroform:methanoland centrifuged for 20 minutes at 13,500 rpm. 62 μL of water was addedto 1 mL homogenate to yield a solution of 20:10:2chloroform:methanol:water. 10 μL pyridine was added to the homogenate togive a final pyridine concentration of 1%. The sample was agitated for24 hours at 48° C. Solvents and water were removed under vacuum using aSpeedVac system. The sample was resuspended in 2.5 mL methanol and 250μL of 1 M KOH in methanol was then added. The sample was then shaken for2 hours at 37° C. The saponification reaction was stopped by theaddition of 10 μL of acetic acid. 2.5 mL chloroform was then added tothe sample, followed by the addition of 2.5 mL cold water. The samplewas vigorously shaken for 5 minutes and was allowed to rest for 5minutes to allow phase separation. The upper phase, composed of methanoland water, was discarded, and the lower phase, composed of chloroformand methanol, was evaporated under vacuum (SpeedVac), and the residuewas resuspended in 300 μL of 1:1 (v/v) chloroform:methanol for analysisof the glycosphingolipids by HPTLC.

Qualitative and semiquantitative analyses of tissue glycolipids wereperformed by high performance thin layer chromatography (HPTLC) (CAMAG,Switzerland). HPTLC analysis was performed on HPTLC silica gel 60 glasscoated plates (Merck). Samples were loaded on the plates using a Linomat5 system (CAMAG, Switzerland). Plates were developed usingchloroform-methanol-water (60:35:4) as the solvent system. Neutralglycosphingolipids were detected with primuline spray reagent. Gb₃ wasidentified using porcine red blood cell Gb₃ (Matreya) as a standard, andquantified using a calibration curve of N-heptadecanoyl ceramidetrihexoside (Matreya), a semi-synthetic standard. Plates were visualizedand relevant spots were quantified using a TLC Scanner III (CAMAG,Switzerland) supported by winCATS software (CAMAG, Switzerland).

SDS-PAGE:

SDS-PAGE was carried out under reduced conditions using a Bio-RadCriterion™ system and in-house casted 12% acrylamide gel. The gel wasstained by Coomassie Blue G250 stain.

IEF (Isoelectric Focusing):

IEF was carried out using an Invitrogen Novex® mini-cell and precastedIEF gels having a pH range of 3-7 (Invitrogen). The gel was stained byCoomassie Blue G250.

Mass Spectrometry (MALDI-TOF):

MALDI-TOF was performed using a Bruker Reflex IV MALDI-ToFMass-spectrometer system (Bruker-Franzen Analytik GmbH, Germany) and asinapinic acid/trifluoroacetic acid (TFA) (0.1% TFA/acetonitrile (2:1,v/v)) saturated matrix solution.

Example I In Vitro Stability of Recombinant α-GAL

The in vitro stability of recombinant α-GAL was measured in variousconditions as described hereinabove in the Materials and MethodsSection. Plant recombinant human α-GAL-I, as well as Fabrazyme® andReplagal® commercial recombinant human α-GAL, were tested.

As shown in FIG. 1, all of the tested types of α-GAL exhibited a loss ofactivity under simulated lysosomal conditions.

In addition, as shown in FIG. 2, all of the tested types of α-GALexhibited a loss of activity under simulated physiological conditions.As further shown therein, the presence of 100 mg/mL galactose partiallyprotected the activity of plant recombinant α-GAL-I under suchconditions.

Similarly, as shown in FIG. 3, all of the tested types of α-GALexhibited a loss of activity in human plasma at 37° C.

As shown in FIG. 4, the presence of 100 mg/mL galactose partiallyprotected the activity of plant recombinant α-GAL-I under simulatedlysosomal conditions.

Size exclusion chromatography (SEC) experiments at lysosomal and neutralpH levels demonstrated changes in the protein structure (data notshown), while SDS-PAGE and Western blot analyses did not exhibit anydegradation of the primary amino acid sequence (data not shown).

These results indicate that α-GAL loses activity under lysosomalconditions and physiological conditions due to alteration of the α-GALprotein structure, and that galactose partially prevents this loss ofactivity.

Example II Cross-Linking of Plant Recombinant Human α-GAL-I withbis-N-hydroxysuccinimide-poly(ethylene glycol) (bis-NHS-PEG) Agents

Plant recombinant human α-GAL-I (prh-α-GAL-I) was cross-linked at 50:1,100:1 and 200:1 molar ratios with bis-N-hydroxysuccinimide-poly(ethyleneglycol) (bis-NHS-PEG) of various molecular weights, namely bis-NHS-PEG₅,bis-NHS-PEG₈ or bis-NHS-PEG₄₅ (bis-NHS-PEG with 2,000 Dalton PEG), thestructures of which are shown in FIG. 5.

The bis-NHS-PEG may attach to the protein at two sites on a protein(e.g., lysine residues), thereby forming cross-linking, or at one siteon a protein. These two forms of attachment are depicted in FIG. 6.

100 μg α-GAL-I in 28.5 μL of 2-(N-morpholino)ethanesulfonic acid (MES)buffer (25 mM, pH 6) was added to 13.5 μL of phosphate buffer (100 mM,pH 8) containing 100 mg/ml galactose.

α-GAL-I was cross-linked with bis-NHS-PEG₅ at 1:50, 1:100, and 1:200protein: reagent molar ratios, by adding bis-NHS-PEG₅ in 8 μL DMSO tothe α-GAL-I solution (27.4 μg α-GAL-I solution for a 1:50 molar ratio,54.8 μg α-GAL-I solution for a 1:100 molar ratio, and 109.7 μg α-GAL-Isolution for a 1:200 molar ratio).

α-GAL-I was cross-linked with bis-NHS-PEG₄₅ at 1:50, 1:100, and 1:200protein: reagent molar ratios, by adding bis-NHS-PEG₄₅ in 8 μL DMSO tothe α-GAL-I solution (103 μg α-GAL-I solution for a 1:50 molar ratio,206 μg α-GAL-I solution for a 1:100 molar ratio, and 412 μg α-GAL-Isolution for a 1:200 molar ratio) α-GAL-I was crosslinked withbis-NHS-PEG₈ at 1:50, 1:100, and 1:200 protein: reagent molar ratios, byadding bis-NHS-PEG₈ in 11.5 μL DMSO to the α-GAL-I solution (37 μgα-GAL-I for a 1:50 molar ratio, 73 μg α-GAL-I solution for a 1:100 molarratio, and 146 μg α-GAL-I solution for a 1:200 molar ratio).

After adding the bis-NHS-PEG agent to the α-GAL-I, the reactions werepipetted and agitated on an orbital shaker for 2 hours at roomtemperature.

In all reactions the excess of bis-NHS-PEG cross-linking reagent wasremoved by dialysis against saline (50 KDa cut off).

The yield of dimer increased with increasing protein concentration andDMSO concentration, reaching up to 30%.

The reaction products were analyzed by SDS-PAGE (sodium dodecylsulfate-polyacrylamide gel electrophoresis), IEF (isoelectric focusing),Western blot, and MALDI-TOF mass spectrometry, as described hereinabove.

As shown in FIG. 7, the standard native prh-α-GAL-I was observed as amonomer (having a molecular weight of 48 KDa) following gelelectrophoresis, whereas following reaction of prh-α-GAL-I withbis-NHS-PEG, prh-α-GAL-I appeared primarily in the form of a dimer (withsome monomer present), indicating that the two monomers were covalentlylinked by cross-linking with bis-NHS-PEG.

As is further shown in FIG. 7, a higher proportion of monomericprh-α-GAL-I was observed with the shorter cross-linkers, bis-NHS-PEG₅and bis-NHS-PEG₅, than with the longer cross-linker bis-NHS-PEG₄₅. Thebis-NHS-PEG₄₅ yielded a high proportion of cross-linked protein. Theseresults indicate that the shorter cross-linkers are less effective atcovalently linking monomers.

As is further shown in FIG. 7, for each of the tested cross-linkers, themolecular weight of the monomeric portion of prh-α-GAL-I increasedfollowing reaction with the cross-linker. The increase in molecularweight was greater when a higher ratio of cross-linker to protein wasused (e.g., 200:1), and when the molecular weight of the cross-linkerwas greater (e.g., bis-NHS-PEG₄₅). These results indicate that proteinmonomers which were not dimerized by cross-linking, were covalentlyattached to the bis-NHS-PEG cross-linker, i.e., the proteins werePEGylated.

The above results indicate that the use of higher molar excess ofcross-linker to protein yields higher levels of α-GAL modification,including both cross-linking to form a dimer and PEGylation of theproteins. However, a molar ratio of 100:1 provided a high level ofcross-linking, especially in the reactions using the bis-NHS-PEG₄₅reagent, such that a molar ratio of 200:1 provided only a marginaladdition to the cross-linking efficiency.

As shown in FIG. 8, reacting prh-α-GAL-I with bis-NHS-PEG reduced theisoelectric point (pI) of prh-α-GAL-I, thereby confirming that thebis-NHS-PEG is covalently attached to the prh-α-GAL-I. Attachment ofbis-NHS-PEG to prh-α-GAL-I converts basic amine groups in lysineresidues to neutral amide groups, thereby reducing the pI. The reductionin pI was more pronounced when a greater molar excess (e.g., 200:1) ofbis-NHS-PEG was used, confirming the above results obtained withSDS-PAGE.

As is further shown in FIG. 8, the pI is reduced more by bis-NHS-PEG₅and bis-NHS-PEG₈ than by bis-NHS-PEG₄₅.

This result indicates that bis-NHS-PEG₅ and bis-NHS-PEG₈ are more likelythan bis-NHS-PEG₄₅ to result in PEGylation in which only one terminus ofthe cross-linker is attached to α-GAL. A cross-linker attached to α-GALat only one terminus is more effective at reducing the pI because such across-linker comprises an acidic carboxylic (—CO₂H) group at thenon-attached terminus, in addition to converting a lysine amine group toan amide group at the attached terminus.

As shown in FIG. 9, reacting prh-α-GAL-I with bis-NHS-PEG₄₅ cross-linkerincreased the molecular weight of the prh-α-GAL-I dimer from 97 KDa to113 KDa, as determined by MALDI-TOF mass spectrometry. The increase inmolecular weight indicates an addition of approximately 8 molecules ofbis-NHS-PEG₄₅ to the prh-α-GAL-I dimer.

As shown in FIG. 10, reacting prh-α-GAL-I with a bis-NHS-PEG₈cross-linker increased the molecular weight of the prh-α-GAL-I dimerfrom 97 KDa to 104 KDa, as determined by MALDI-TOF mass spectrometry.The increase in molecular weight indicates an addition of approximately10 molecules of bis-NHS-PEG₈ to the prh-α-GAL-I dimer.

Example III Activity of Cross-Linked Plant Recombinant Human α-GAL-I

In order to determine whether the cross-linked plant recombinant α-GAL-I(prh-α-GAL-I) described in Example II retained enzymatic activity, thecross-linked prh-α-GAL-I was assayed for its enzymatic activity usingthe 4-methylumbelliferyl-α-D-galactopyranoside assay describedhereinabove.

As shown in Table 1 below, prh-α-GAL-I which was reacted withbis-NHS-PEG₅, bis-NHS-PEG₅ or bis-NHS-PEG₄₅ at molar excesses of 50:1,100:1 and 200:1 bis-NHS-PEG reagent in all cases exhibited a level ofenzymatic activity similar to that of native prh-α-GAL-I. As showntherein, both moderate decreases and moderate increases in activity wereobserved in some cases, which may be a result of formulation effects.These results indicate that the cross-linking did not reduce theactivity of prh-α-GAL-I.

TABLE 1 Activity results of cross-linked plant recombinant human α-GAL IActivity Sample Reagent Molar excess mg/mL standard — — 2 1 Bis-NHS-PEG₅ 50:1 2.25 2 Bis-NHS-PEG₅ 100:1 1.30 3 Bis-NHS-PEG₅ 200:1 1.24 4Bis-NHS-PEG₄₅  50:1 2.82 5 Bis-NHS-PEG₄₅ 100:1 2.76 6 Bis-NHS-PEG₄₅200:1 3.48 7 Bis-NHS-PEG₈  50:1 2.18 8 Bis-NHS-PEG₈ 100:1 2.43 9Bis-NHS-PEG₈ 200:1 1.82

The activity of the bis-NHS-PEG₄₅ cross-linked prh-α-GAL-I was furtherverified using the N-dodecanoyl-NBD-ceramide trihexoside assay describedhereinabove, which assays the activity of α-GAL towards its naturalsubstrate, ceramide trihexoside (Gb₃). Replagal® mammalian recombinanthuman α-GAL was assayed for comparison.

As shown in FIG. 11, following incubation of the cross-linked plantrecombinant human α-GAL-I with the fluorescent substrate, almost allsubstrate was converted to the product,N-dodecanoyl-nitrobenzoxadiazole-lactosyl ceramide, similarly to thereaction catalyzed by the mammalian recombinant α-GAL (Replagal®). Thisresult confirms that the cross-linking did not impair the enzymatichydrolytic efficiency of the prh-α-GAL-I, using a close analog of thenatural substrate.

Example IV In Vitro Stability of Cross-Linked Plant Recombinant Humanα-GAL-I

The in vitro stability of the cross-linked plant recombinant humanα-GAL-I (prh-α-GAL-I), obtained as described in Example II, was measuredin various conditions as described hereinabove in the Materials andMethods Section. The stability of Fabrazyme® and Replagal® commercialrecombinant human α-GALs was measured for comparison.

As shown in FIGS. 12A-12C, the stability of plant recombinant humanα-GAL-I under simulated lysosomal conditions was enhanced bycross-linking with bis-NHS-PEG₅ (FIG. 12A), bis-NHS-PEG₈ (FIG. 12B) andbis-NHS-PEG₄₅ (FIG. 12C). As further shown therein, the stability of thecross-linked prh-α-GAL-I over the course of one week compared favorablyto the stability of the commercial recombinant human α-GAL. After asmall decrease in residual activity during the first 24 hours, thecross-linked prh-α-GAL-I maintained activity, even after 10 days. Theinitial decrease in activity, observed during the first 24 hours, mayreflect the portion of plant recombinant human α-GAL-I that did notundergo cross-linking.

As further shown in FIGS. 12A-12C, prh-α-GAL-I cross-linked bybis-NHS-PEG₄₅ exhibited the highest stability under simulated lysosomalconditions.

The stability of plant recombinant human α-GAL-I in human plasma at 37°C. was also enhanced by cross-linking with bis-NHS-PEG₄₅ (data notshown).

These results indicate that cross-linking α-GAL as described herein canincrease the efficacy of α-GAL in vivo by increasing the stability ofα-GAL in lysosomes, thereby allowing α-GAL to act for a longer period oftime in the lysosomes, and by increasing the stability of α-GAL in theblood, thereby increasing the circulatory half-life of α-GAL.

Example V In Vivo Pharmacokinetics and Bio-Distribution of Cross-LinkedPlant Recombinant Human α-GAL-I

The pharmacokinetics and bio-distribution of plant recombinant humanα-GAL-I (prh-α-GAL-I) cross-linked with bis-NHS-PEG₄₅ or bis-NHS-PEG₈ asdescribed in Example II was determined in Fabry mice injected with 2mg/Kg of α-GAL, as described hereinabove in the Materials and MethodsSection. The pharmacokinetics and bio-distribution of non-cross-linkedplant recombinant human α-GAL-I and of Replagal® recombinant human α-GALwas determined for comparison. Blood samples were collected forpharmacokinetic analysis 1, 3, 5, 10, 20, 30, 40, 60 and 120 minutespost-injection. For each type of α-GAL, the treatment group consisted ofsix mice.

As shown in Table 2 below, cross-linking prh-α-GAL-I with bis-NHS-PEG₈and with bis-NHS-PEG₄₅ increased the circulatory terminal half-life ofplant recombinant human α-GAL-I, with the latter exhibiting a morepronounced effect.

TABLE 2 Circulatory terminal half-lives of recombinant α-GAL α-GALsample t_(1/2) (minutes) Replagal ® mammalian recombinant human α-GAL8.1 Plant recombinant human α-GAL-I 4.8 Plant recombinant human α-GAL Icross-linked with 6.2 bis-NHS-PEG₈ Plant recombinant human α-GAL-Icross-linked with 90 bis-NHS-PEG₄₅

As shown in FIG. 13 and in Table 2, the terminal half-life of prhα-GAL-I cross-linked by bis-NHS-PEG₄₅ was considerably greater than theterminal half-life of Replagal® α-GAL.

As further shown in FIG. 13, the activity of plant recombinant humanα-GAL-I cross-linked with bis-NHS-PEG₄₅ at 20 minutes was about 40% ofthe activity at 1 minute. Furthermore, the cross-linked prh-α-GAL-Iexhibited an active plasma presence even 4 hours post-injection.

These results indicate that the cross-linked prh-α-GAL-I remains activein vivo for a relative long time, which can allow the enzyme to reachadditional tissues and organs.

As shown in FIGS. 14A and 14B, the levels of plant recombinant α-GAL-Icross-linked with bis-NHS-PEG₈ and bis-NHS-PEG₄₅ in the spleens of Fabrymice 2 hours post-injection were considerably higher than those ofnon-cross-linked plant recombinant α-GAL-I as well those of Replagal®mammalian recombinant α-GAL. As further shown therein, levels ofprh-α-GAL-I cross-linked with bis-NHS-PEG₄₅ were higher than levels ofprh-α-GAL-I cross-linked with bis-NHS-PEG₈. The Western blot analyses(FIG. 14B) are consistent with the bio-distribution results obtained byassaying α-GAL enzymatic activity (FIG. 14A).

As shown in FIGS. 15A and 15B, the levels of plant recombinant α-GAL-Icross-linked with bis-NHS-PEG₈ and bis-NHS-PEG₄₅ in the livers of Fabrymice 2 hours post-injection were considerably higher than those ofnon-cross-linked plant recombinant α-GAL-I, but lower than levels ofReplagal® mammalian recombinant α-GAL in the liver. As further showntherein, levels of prh-α-GAL-I cross-linked with bis-NHS-PEG₄₅ wereslightly higher than levels of prh-α-GAL-I cross-linked withbis-NHS-PEG₈. The Western blot analyses (FIG. 15B) are consistent withthe bio-distribution results obtained by assaying α-GAL enzymaticactivity (FIG. 15A).

Lower levels of α-GAL in the liver may be therapeutically advantageous,as about 95% of the recovered enzyme in enzyme replacement therapy istypically found in the liver, and hence high levels of recombinant α-GALin the liver indicate lower levels of exogenous α-GAL in target organs,such as heart and kidneys.

As shown in FIG. 16, the levels of plant recombinant α-GAL-Icross-linked with bis-NHS-PEG₈ and bis-NHS-PEG₄₅ in the hearts of Fabrymice 2 hours post-injection were higher than those of non-cross-linkedplant recombinant α-GAL-I. As further shown therein, levels ofprh-α-GAL-I cross-linked with bis-NHS-PEG₄₅ were higher than levels ofprh-α-GAL-I cross-linked with bis-NHS-PEG₈, as well as levels ofReplagal® mammalian recombinant α-GAL.

As shown in FIG. 17, the levels of plant recombinant α-GAL-Icross-linked with bis-NHS-PEG₈ and bis-NHS-PEG₄₅ in the kidneys of Fabrymice 2 hours post-injection were higher than those of non-cross-linkedplant recombinant α-GAL-I. As further shown therein, levels ofprh-α-GAL-I cross-linked with bis-NHS-PEG₄₅ were higher than levels ofprh-α-GAL-I cross-linked with bis-NHS-PEG₈, as well as levels ofReplagal® mammalian recombinant α-GAL.

Similarly, as shown in FIGS. 18-21, the levels of plant recombinantα-GAL-I cross-linked with bis-NHS-PEG₄₅ were higher than the levels ofnon-cross-linked plant recombinant α-GAL-I in the spleen (FIG. 18),liver (FIG. 19), heart (FIG. 20) and kidneys (FIG. 21) of Fabry mice,for up to 7 days post-injection. As further shown therein, the levels ofplant recombinant α-GAL-I cross-linked with bis-NHS-PEG₄₅ were higherthan the levels of Replagal® mammalian recombinant α-GAL in the spleen,heart and kidneys.

These results indicate that α-GAL cross-linked with bis-NHS-PEG,particularly bis-NHS-PEG₄₅, exhibits enhanced uptake into organs,including the kidney and heart, which are major target organs in thetreatment of Fabry disorder. These results are consistent with theincreased circulatory half-life and enhanced stability of cross-linkedα-GAL.

Example VI Cross-Linking of Mammalian Recombinant Human α-GAL withBis-N-Hydroxysuccinimide-Poly(Ethylene Glycol) (Bis-NHS-PEG)

In order to confirm the advantageous effects of cross-linking describedhereinabove, Replagal® mammalian recombinant human α-GAL, which isproduced from human fibrosarcoma line HT-1080, was cross-linked.

333 μL of phosphate buffer (100 mM, pH 8) with 100 mg/ml D-(+)-galactosewas added to 3.8 mg bis-NHS-PEG₄₅ in 151 μL of DMSO solution (25 mg/ml)and 1.8 mg of Replagal® recombinant human α-GAL in 130 μL citrate buffer(25 mM, pH 6). Replagal® α-GAL concentration was determined by anactivity assay. The reaction mixture was agitated using an orbitalshaker for 2 hours at room temperature. The excess of bis-NHS-PEG₄₅cross-linking reagent was removed by dialysis against saline using aVivaspin 6 concentrator with a cut-off of 50 KDa. The α-GAL activity ofthe cross-linked Replagal® α-GAL indicated that the α-GAL concentrationwas 3 mg/mL.

The reaction products were analyzed by SDS-PAGE (sodium dodecylsulfate-polyacrylamide gel electrophoresis), IEF (isoelectric focusing),and MALDI-TOF mass spectrometry, as described hereinabove.

As shown in FIG. 22, the standard native Replagal® α-GAL was observed asa monomer following gel electrophoresis, whereas following reaction ofReplagal® α-GAL with bis-NHS-PEG₄₅, the α-GAL appeared in the form of adimer, indicating that the two monomers were covalently linked bycross-linking with bis-NHS-PEG.

As shown in FIG. 23, reacting Replagal® α-GAL with bis-NHS-PEG₄₅ reducedthe isoelectric point (pI) of the α-GAL, thereby confirming that thebis-NHS-PEG is covalently attached to the α-GAL.

As shown in FIG. 24, reacting Replagal® α-GAL with bis-NHS-PEG₄₅cross-linker increased the molecular weight of the Replagal® α-GAL dimerfrom 103.0 KDa to 121.3 KDa, as determined by MALDI-TOF massspectrometry. The increase in molecular weight indicates an addition ofapproximately 9-10 molecules of bis-NHS-PEG₄₅ to the α-GAL dimer, whichis similar to results described hereinabove for prh-α-GAL-I.

Example VII Activity of Cross-Linked Mammalian Recombinant Human α-GAL

In order to determine whether the cross-linking of mammalian recombinantα-GAL described in Example VI affected enzymatic activity, thecross-linked α-GAL was assayed for its enzymatic activity using ap-nitrophenyl-α-D-galactopyranoside (pNP-G) assay, according to theprocedures described hereinabove.

As shown in FIG. 25 and in Table 3 below, mammalian recombinant humanα-GAL which was cross-linked with bis-NHS-PEG₄₅ exhibited parameters ofenzymatic activity which are very similar to those of native mammalianrecombinant human α-GAL. These results indicate that the cross-linkingdid not significantly affect the activity or the catalytic machinery andmechanism of the mammalian recombinant human α-GAL.

TABLE 3 Activity results of cross-linked mammalian recombinant humanα-GAL K_(M) V_(max) k_(cat) k_(cat)/K_(M) Sample (μM) (μM/minute)(second⁻¹) (second⁻¹*μM⁻¹) Replagal ® 3212 ± 98  4.20 ± 0.05 67.2 ± 10.0209 ± 0.001 α-GAL Cross-linked 3419 ± 162 4.43 ± 0.07 70.9 ± 1 0.0210± 0.001 Replagal ® α-GAL

Example VIII In Vitro Stability of Cross-Linked Mammalian RecombinantHuman α-GAL

The in vitro stability of the cross-linked Replagal® mammalianrecombinant human α-GAL, obtained as described in Example VI, wasmeasured in various conditions as described hereinabove in the Materialsand Methods Section. The stability of non-cross-linked Replagal® α-GALwas measured for comparison, in order to assess the effect ofcross-linking.

As shown in FIGS. 26A and 26B, the stability of mammalian recombinanthuman α-GAL under both simulated lysosomal conditions (FIG. 26A) and inhuman plasma (FIG. 26B) was considerably enhanced by cross-linking withbis-NHS-PEG₄₅. The cross-linked mammalian recombinant human α-GALexhibited higher stability under simulated lysosomal conditions than inplasma.

These results indicate that the cross-linking of α-GAL as describedherein can stabilize recombinant α-GAL from multiple sources andexpression platforms.

Example IX In Vivo Pharmacokinetics and Bio-Distribution of Cross-LinkedMammalian Recombinant Human α-GAL

The pharmacokinetics and bio-distribution of the cross-linked mammalianrecombinant human α-GAL described in Example VI was determined bymeasuring α-GAL activity in the spleen, liver, heart and kidneys ofFabry mice 2 hours, 7, 14, and 28 days post-injection, as well as Gb₃levels in these organs, as described hereinabove in the Materials andMethods section. The bio-distribution of non-cross-linked Replagal®mammalian recombinant human α-GAL was determined for comparison.

As shown in FIGS. 27A-27D, the levels of cross-linked mammalianrecombinant α-GAL in the spleens (FIG. 27A), liver (FIG. 27B), heart(FIG. 27C) and kidneys (FIG. 27D) of Fabry mice were considerably higherthan those of non-cross-linked mammalian recombinant α-GAL.

As shown in FIGS. 28A-28D, cross-linked mammalian recombinant α-GALdecreased Gb₃ levels in the heart (FIG. 28A), kidney (FIG. 28B), liver(FIG. 28C) and spleen (FIG. 28D) of Fabry mice, over the course of 28days post-injection. Cross-linked mammalian recombinant α-GAL decreasedGb₃ levels to a greater extent than did non-cross-linked recombinantα-GAL in the kidney (FIG. 28B) and spleen (FIG. 28D) of Fabry mice, andto about the same extent as non-cross-linked mammalian recombinant α-GALin the heart (FIG. 28A) and liver (FIG. 28C).

These results indicate that cross-linking with bis-NHS-PEG results inconsiderably enhanced uptake of recombinant α-GAL from a variety ofsources and expression platforms into organs, including the kidney andheart, which are major target organs in the treatment of Fabry disorder.These results further indicate that cross-linking with bis-NHS-PEGresults in a more substantial decrease of Gb₃ levels in organs.

Example X Cross-Linking of Plant Recombinant Human α-GAL-II withBis-N-Hydroxysuccinimide-Poly(Ethylene Glycol) (Bis-NHS-PEG)

Plant recombinant human α-GAL-II (prh-α-GAL-II), which lacks the aminoacids EF present in the N-terminus of prh-α-GAL-I, was cross-linked withbis-NHS-PEG₄₅, bis-NHS-PEG₂₁, or bis-NHS-PEG₆₈ at a 200:1 molar ratio ofbis-NHS-PEG to α-GAL, according to the protocol described in Example II.

The prh-α-GAL-II retained its biological activity followingcross-linking with bis-NHS-PEG (data not shown).

The reaction products were analyzed by SDS-PAGE (sodium dodecylsulfate-polyacrylamide gel electrophoresis) and MALDI-TOF massspectrometry, as described hereinabove.

As shown in FIGS. 29A-29B, the standard native prh-α-GAL-II was observedas a monomer following gel electrophoresis, whereas following reactionof prh-α-GAL-II with bis-NHS-PEG₄₅ or bis-NHS-PEG₂₁ (FIG. 29A), or withbis-NHS-PEG₆₈ (FIG. 29B), prh-α-GAL-II appeared primarily in the form ofa dimer (with some monomer present), indicating that the two monomerswere covalently linked by cross-linking with a bis-NHS-PEG cross-linkingagent.

As is further shown in FIGS. 29A-29B, for each of the testedcross-linkers, the molecular weight of the monomeric portion ofprh-α-GAL-II increased following reaction with the cross-linker. Theincrease in molecular weight was greater for bis-NHS-PEG₄₅ than forbis-NHS-PEG₂₁ (FIG. 29A), and was greatest for bis-NHS-PEG₆₈ (compareFIG. 29A with FIG. 29B). These results indicate that the monomers whichwere not dimerized by cross-linking, were covalently attached to thebis-NHS-PEG cross-linker, i.e., the proteins were PEGylated.

As shown in FIGS. 30A-30C, reacting prh-α-GAL-II with bis-NHS-PEG₂₁cross-linker increased the molecular weight of the prh-α-GAL-II dimerfrom 95 KDa (FIG. 30A) to 109 KDa (FIG. 30B), while reactingprh-α-GAL-II with bis-NHS-PEG₄₅ cross-linker increased the molecularweight of the prh-α-GAL-II dimer to 114 KDa (FIG. 30C), as determined byMALDI-TOF mass spectrometry. The increase in molecular weight indicatesan addition of approximately 13 molecules of bis-NHS-PEG₂₁, orapproximately 9 molecules of bis-NHS-PEG₄₅, to the prh-α-GAL-II dimer.

Example XI In Vitro Stability of Cross-Linked Plant Recombinant Humanα-GAL-II

The in vitro stability of the cross-linked plant recombinant humanα-GAL-II (prh-α-GAL-II) obtained as described in Example X was measuredunder various conditions as described hereinabove in the Materials andMethods Section. The stability of Replagal® commercial recombinant humanα-GAL was measured for comparison.

As shown in FIGS. 31A-31D, the stability of plant recombinant humanα-GAL-II was enhanced by cross-linking with either bis-NHS-PEG₆₈ (FIGS.31B and 31D), bis-NHS-PEG₄₅ (FIGS. 31A-31D) or bis-NHS-PEG₂₁ (FIGS. 31Aand 31C), under both simulated lysosomal conditions (FIGS. 31A and 31B)and in human plasma (FIGS. 31C and 31D). The different cross-linkersenhanced the stability of prh-α-GAL-II to comparable extents. As furthershown therein, the stability of the cross-linked prh-α-GAL-II wasgreater than the stability of the Replagal® recombinant human α-GAL. Thecross-linked prh-α-GAL-II exhibited higher stability under simulatedlysosomal conditions as well as under plasma conditions.

As further shown in FIGS. 31A-31D, non-cross-linked prh-α-GAL-II isconsiderably more stable than non-cross-linked prh-α-GAL-I (see FIGS. 1and 3 for comparison), under both simulated lysosomal conditions (FIGS.1 and 31A-31B) and in human plasma (FIGS. 3 and 31C-31D), althoughprh-α-GAL-II still exhibits some instability.

These results indicate that the cross-linking of α-GAL as describedherein can stabilize different types of α-GALs.

Example XII In Vivo Pharmacokinetics and Bio-Distribution ofCross-Linked Plant Recombinant Human α-GAL-II

The pharmacokinetics and bio-distribution of the PEG₄₅-cross-linked andPEG₂₁-cross-linked plant recombinant human α-GAL-II (prh-α-GAL-II),described in Example X, was determined by measuring α-GAL activity inplasma and organs as described hereinabove in the Materials and Methodssection. The pharmacokinetics and bio-distribution of non-cross-linkedReplagal® mammalian recombinant human α-GAL were determined forcomparison.

Blood samples were collected for pharmacokinetic analyses at 1, 5, 10,30, 60, 120, 240, 480 and 1440 minutes after injection of Fabry micewith 1 mg/Kg of α-GAL.

Bio-distribution of α-GAL was determined by harvesting the liver,kidneys, heart and spleen of Fabry mice 2 hours, 7 days, 14 days and 28days post-injection with 2 mg/Kg α-GAL.

As shown in FIGS. 32A and 32B and in Table 4, cross-linking ofprh-α-GAL-II with bis-NHS-PEG₄₅ considerably increased the circulatoryterminal half-life of prh-α-GAL-II, yielding a circulatory half-lifeconsiderably greater than that of mammalian recombinant α-GAL or ofnon-cross-linked prh-α-GAL-II.

TABLE 4 Circulatory terminal half-life of recombinant α-GAL Test itemt_(1/2) (min) Replagal ® α-GAL 13.3 plant recombinant alpha-GAL-II 4.8plant recombinant alpha-GAL-II cross- 581.6 linked with bis-NHS-PEG₄₅

As shown in FIGS. 33A-33L, cross-linking of prh-α-GAL-II withbis-NHS-PEG₄₅ increased the uptake of prh-α-GAL-II in heart (FIG. 33A),kidney (FIG. 33B), liver (FIG. 33C) and spleen (FIG. 33D) of Fabry mice,although to a lesser degree in the liver.

As shown in FIGS. 33E-33L, cross-linking of prh-α-GAL-II withbis-NHS-PEG₂₁ also increased the uptake of prh-α-GAL-II in heart (FIGS.33E and 33I), kidney (FIGS. 33F and 33J), liver (FIGS. 33G and 33K) andspleen (FIGS. 33H and 33L) of Fabry mice, although such an increase wasnot always evident after only 2 hours.

As further shown therein, the levels of cross-linked prh-α-GAL-II weregreater than the levels of mammalian recombinant α-GAL in the heart(FIGS. 33A, 33E and 33I), kidney (FIGS. 33B, 33F and 33J), and spleen(FIGS. 33D, 33H and 33L) of Fabry mice, and lower than the levels ofmammalian recombinant α-GAL in the liver (FIGS. 33C, 33G and 33K).

These results indicate that cross-linked prh-α-GAL-II exhibitsconsiderably enhanced activity of α-GAL in the plasma and in variousorgans, particularly in organs other than the liver.

Example XIII Effect of pH on Activity of Plant Recombinant Human α-GAL

The pH of the environment has a significant effect on the stability andkinetics of lysosomal enzymes such α-GAL. The pH may affect binding ofsubstrate to the enzyme. The pH can also affect the protonation ordeprotonation of catalytic groups, such as carboxyl or amino groups,which are part of the enzyme's active site, and thus affect the kineticbehavior of the enzyme. The stability of the tertiary or quaternarystructure of enzymes is also pH-dependent, and affects the velocity ofthe enzymatic reaction, especially at extremely acidic or alkaline pHvalues.

The activity of PEG₄₅-cross-linked and non-cross-linked plantrecombinant human α-GAL-II was determined at various pH values using apNP-G substrate, in order to examine the pH-dependence of α-GALactivity, and the effect of cross-linking thereon. The measurements wereperformed in solutions of 20 mM citrate and 30 mM sodium phosphate.

The kinetic parameters characterizing α-GAL activity at various pHvalues are summarized in Table 5 below, and in FIGS. 34A-34C.

As shown in FIGS. 34A-34C, cross-linking of the α-GAL-II increased theV_(max) (FIG. 34A) and k_(cat) (FIG. 34C) parameters, and did not have asignificant effect on the K_(M) parameter (FIG. 34B).

TABLE 5 Activity results of non-cross-linked plant recombinant humanα-GAL-II (prh-α-GAL-II) and PEG₄₅-cross-linked plant recombinant humanα-GAL II (prh-α-GAL-II-CL45) at various pH values K_(M) V_(max) k_(cat)k_(cat)/K_(M) pH Sample (μM) (μM/minute) (second⁻¹) (second⁻¹*μM⁻¹) 2.8prh-α-GAL-II 15216 0.57 9.04 0.0006 prh-α-GAL-II-CL45 13618 0.90 14.370.0011 3.2 prh-α-GAL-II 11476 0.55 8.85 0.0008 prh-α-GAL-II-CL45 84891.34 21.44 0.0025 3.6 prh-α-GAL-II 11147 1.76 28.16 0.0025prh-α-GAL-II-CL45 4699 2.23 35.68 0.0076 4.04 prh-α-GAL-II 5709 1.9831.68 0.0055 prh-α-GAL-II-CL45 3207 2.74 43.76 0.0136 4.4 prh-α-GAL-II4596 2.40 38.40 0.0084 prh-α-GAL-II-CL45 3122 3.22 51.57 0.0165 4.8prh-α-GAL-II 4531 2.32 37.12 0.0082 prh-α-GAL-II-CL45 3345 2.95 47.230.0141 5.29 prh-α-GAL-II 6793 2.06 32.99 0.0049 prh-α-GAL-II-CL45 39732.78 44.48 0.0112 5.66 prh-α-GAL-II 10396 1.75 28.05 0.0027prh-α-GAL-II-CL45 4883 2.70 43.20 0.0088 6.09 prh-α-GAL-II 11357 1.4423.04 0.0020 prh-α-GAL-II-CL45 8336 1.54 24.59 0.0030 6.4 prh-α-GAL-II21046 1.32 21.12 0.0010 prh-α-GAL-II-CL45 16844 1.46 23.36 0.0014 6.76prh-α-GAL-II 25188 1.12 17.92 0.0007 prh-α-GAL-II-CL45 18313 1.14 18.240.0010 7.36 prh-α-GAL-II — — — — prh-α-GAL-II-CL45 32692 0.52 8.370.0003

The enhancement of the V_(max) and k_(cat) parameters indicates anincrease in catalytic activity. This increase is particularlysignificant at pH values of at least about 7, where the catalyticactivity of non-cross-linked α-GAL-II is negligible.

K_(M) is a kinetic parameter associated with enzyme/substrate affinity.The absence of a significant effect of cross-linking on K_(M) valuesindicates that the cross-linking has no significant effect on α-GALaffinity to the pNP-G substrate.

Example XIV Effect of PEGylation on Stability of α-GAL

The effect of PEGylation per se on α-GAL stability was ascertained, inorder to determine whether the stabilizing effect of PEG cross-linkersis due to the properties of PEG or due to the cross-linking.

Plant recombinant human α-GAL-I was reacted with N-hydroxysuccinimide(NHS)-activated methoxy-capped PEGs with different molecular weights (2,5, and 10 KDa). Such PEG reagents have a single NHS group, andconsequently PEGylate the protein without forming cross-linking. Thereaction products were analyzed by SDS-PAGE.

As shown in FIG. 35, the methoxy-capped PEGylating agents PEGylated theα-GAL (visible as an increase in molecular weight of the α-GAL), but didnot substantially generate α-GAL dimers, indicating that the α-GAL wasnot cross-linked.

As shown in FIGS. 36A and 36B, PEGylating plant recombinant humanα-GAL-I without forming cross-linking did not substantially increase thestability of the plant recombinant α-GAL, under either simulatedlysosomal conditions (FIG. 36A) or in human plasma (FIG. 36B).

These results indicate that the stabilizing effect of the cross-linkingdescribed hereinabove is not a result of PEGylation per se.

Example XV Effect of PEG Chain Length on Activity of Cross-Linked α-GAL

In order to assess the effect of the chain length of PEG cross-linkerson α-GAL activity, plant recombinant human α-GAL-I was cross-linked withbis-NHS-PEG₂, bis-NHS-PEG₄, bis-NHS-PEG₆₈ and bis-NHS-PEG₁₅₀ agents,using essentially the same procedures as described in Example II (PEG₆₈and PEG₁₅₀ are approximate chain lengths). The α-GAL-I was cross-linkedat 50:1, 100:1 and 200:1 bis-NHS-PEG:α-GAL molar ratios. The reactionproducts were analyzed by SDS-PAGE, as described hereinabove. α-GAL-Icross-linked with bis-NHS-PEG₄₅ as described in Example II was alsoanalyzed for comparison.

As shown in FIG. 37, SDS-PAGE analysis showed that all of thebis-NHS-PEG agents cross-linked the α-GAL so as to result in acovalently cross-linked dimer, and that cross-linking was more efficientwhen a 200:1 molar ratio was used.

The enzymatic activity of the cross-linked α-GAL-I was then determinedas described in Example III. The results are summarized in Table 6below.

TABLE 6 Activity results of cross-linked plant recombinant human α-GAL-IExpected Measured α-GAL α-GAL Molar ratio activity activity Reagent(reagent : α-GAL-I) [mg/mL] [mg/mL]

 50:1 100:1 200:1 2 2 2 1.159 1.001 0.970 bis-NHS-PEG₄  50:1 2 1.399100:1 2 1.333 200:1 2 1.048 bis-NHS-PEG₆₈  50:1 2 1.822 100:1 2 2.252200:1 2 2.425 bis-NHS-PEG₁₅₀  50:1 2 1.804 100:1 2 2.031 200:1 2 1.825

As shown in Table 6, cross-linking with PEG₂ and PEG₄ moderately reducedα-GAL activity (by approximately 30-50%), whereas cross-linking withlonger PEG chains did not significantly affect α-GAL activity.

These results indicate that cross-linking with PEG chains longer thanPEG₄ is advantageous in terms of preserving activity of the cross-linkedα-GAL.

Example XVI Cross-Linking of α-GAL Using Bis-COOH-PEG Agents

As an alternative to the above-described cross-linking of α-GAL usingpre-prepared (e.g., commercially available) bis-NHS-PEG agents, α-GALwas cross-linked with bis-COOH-PEG agents by activating the carboxyl(i.e., COOH) groups in situ shortly before the cross-linking reactionwas effected.

Bis-COOH-PEG₁₂, bis-COOH-PEG₂₈ and bis-COOH-PEG₄₅ were each activated bybeing reacted with 1.1 molar equivalents per carboxyl group (i.e., 2.2molar equivalents per bis-COOH-PEG) of both NHS (N-hydroxysuccinimide)and EDC (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide). The reactionmixture was then shaken in DMSO for 30 minutes at room temperature. Theactivated bis-COOH-PEG, which is essentially bis-NHS-PEG, was thenreacted with plant recombinant human α-GAL-I at molar ratios of 50:1,100:1 and 200:1, as described in Example II. The reaction products wereanalyzed by SDS-PAGE, as described hereinabove. α-GAL-I cross-linkedwith bis-NHS-PEG₄₅ as described in Example II was also analyzed forcomparison.

As shown in FIG. 38, SDS-PAGE analysis showed that all of thebis-COOH-PEG agents cross-linked the α-GAL to some extent, but thatcross-linking was more efficient when a 200:1 molar ratio was used.

The enzymatic activity of the cross-linked α-GAL-I was then determinedas described in Example III. The results are summarized in Table 7below.

TABLE 7 Activity results of cross-linked plant recombinant human α-GAL-IExpected Measured α-GAL α-GAL Molar ratio activity activity Reagent(reagent:α-GAL-I) [mg/mL] [mg/mL] Bis-HOOC-PEG₁₂  50:1 1.5 1.236 100:11.5 1.304 200:1 1.5 1.404 Bis-HOOC-PEG₂₈  50:1 1.5 1.326 100:1 1.5 1.371200:1 1.5 1.460 Bis-HOOC-PEG₄₅  50:1 1.5 1.349 100:1 1.5 1.541 200:1 1.51.628

As shown in Table 7, cross-linking with each of the tested bis-COOH-PEGagents resulted in α-GAL with about the expected activity.

These results indicate that cross-linking bis-COOH-PEG agents does notreduce α-GAL activity in comparison to cross-linking with bis-NHS-PEGagents.

These results further confirm the above-described findings thatcross-linking with PEG chains longer than PEG₄ does not significantlyreduce the activity of the cross-linked α-GAL.

Example XVII Effect of Length and Type of Cross-Linking Agent on InVitro Stability of Cross-Linked Plant Recombinant Human α-GAL-I

In order to further characterize the effect of chain length oncross-linked α-GAL stability, and to compare the stability of α-GALcross-linked with bis-COOH-PEG agents (e.g., as described in ExampleXVI) with that of α-GAL cross-linked with bis-NHS-PEG agents, the invitro stability of plant recombinant human α-GAL-I (prh-α-GAL-I)cross-linked with bis-NHS-PEG₂, bis-NHS-PEG₄, bis-COOH-PEG₁₂,bis-COOH₂₈, and bis-COOH-PEG₄₅, obtained as described in Examples XV andXVI, was measured in various conditions as described hereinabove in theMaterials and Methods Section, and compared with the stability ofprh-α-GAL-I cross-linked with bis-NHS-PEG₄₅ as described in Example II.The stability of Replagal® commercial recombinant human α-GAL andnon-crosslinked prh-GAL-I was measured for comparison.

As shown in FIG. 39, the stability of plant recombinant human α-GAL-Iunder simulated lysosomal conditions was enhanced by cross-linking witheach of the bis-NHS-PEG and bis-COOH-PEG agents.

As further shown therein, the stability of the cross-linked prh-α-GAL-Iwas correlated with the length of the cross-linking PEG chain, withbis-NHS-PEG₄₅ and bis-COOH-PEG₄₅ providing the most stability, andbis-NHS-PEG₂ providing the least stability. However, cross-linking withbis-COOH-PEG₄₅ provided only marginally more stability than didcross-linking with bis-COOH-PEG₄₅, suggesting that above a certainlength, the stability is not affected by PEG chain length.

As further shown in FIG. 39, cross-linking with bis-NHS-PEG₄₅ providedslightly more stability than did cross-linking with bis-COOH-PEG₄₅. Thismay be a result of incomplete activation of the bis-COOH-PEG agent.However the difference in stability was slight.

In addition, cross-linking with each of the bis-NHS-PEG and bis-COOH-PEGagents enhanced the stability of the plant recombinant human α-GAL-I inhuman plasma at 37° C. (data not shown).

These results provide further evidence that cross-linking α-GAL asdescribed herein can increase the efficacy of α-GAL in vivo byincreasing the stability of α-GAL in lysosomes and in the blood, andthat PEG chains of about 28-45 units in length are more effective atstabilizing α-GAL by cross-linking than are shorter PEG chains.

Example XVIII Kinetic Parameters of Cross-Linked Plant Recombinant Humanα-GAL-II

The kinetic parameters of cross-linked plant recombinant human α-GAL-II,obtained as described in Example X, as well as of non-cross-linked plantrecombinant human α-GAL-II, were determined using a pNP-G substrate andMichaelis-Menten analysis, in order to examine the effect ofcross-linking thereon. The measurements were performed in a solution of20 mM citrate, 30 mM sodium phosphate, 0.1% bovine serum albumin and0.67% ethanol, at a pH of 4.6. The kinetic parameters were calculatedusing protein content values based on an activity assay.

As shown in Table 8 below, cross-linking of α-GAL-II resulted inimproved kinetic properties, as compared with non-cross-linked α-GAL-II.The Michaelis constant (K_(M)) was reduced, indicating higher affinityof the enzyme to the substrate. Furthermore, the k_(cat)/K_(m), whichsignifies the overall catalytic efficiency of the enzyme with thissubstrate under the described conditions, was enhanced for thecross-linked species.

TABLE 8 Michaelis-Menten parameters of non-cross-linked plantrecombinant human α-GAL-II (prh-α-GAL-II) and plant recombinant humanα-GAL II cross-linked with bis-NHS-PEG₂₁ (prh-α-GAL-II-CL21),bis-NHS-PEG₄₅ (prh-α-GAL-II-CL45) or bis-NHS-PEG₆₈ (prh-α-GAL-II-CL68)K_(m) V_(max) k_(cat) k_(cat)/K_(m) Sample (μM) (μM/min) (sec⁻¹) (sec⁻¹μM⁻¹) prh-α-GAL-II 4801 4.59 73.49 0.015 prh-α-GAL-II-CL21 2661 4.8577.55 0.029 prh-α-GAL-II-CL45 2583 4.87 77.87 0.030 prh-α-GAL-II-CL682556 4.12 65.97 0.026

Example XIX Reproducibility of Cross-Linking of Plant Recombinant Humanα-GAL-II

The batch-to-batch reproducibility of cross-linking was assessed afterpreparing 5 batches of plant recombinant human α-GAL-II (prh-α-GAL-II)cross-linked with bis-NHS-PEG₄₅ at a 200:1 ratio, using proceduressimilar to those described in Example II.

In batches 1, 2, 4 and 5, 1 mg of prh-α-GAL-II was reacted with 3.98 mgbis-NHS-PEG.

In batch 3, 20.5 mg of prh-α-GAL-II was reacted with 80.7 mgbis-NHS-PEG.

The enzymatic activity of the cross-linked prh-α-GAL-II was determinedas described in Example III. The results are summarized in Table 9below.

TABLE 9 Activity results of cross-linked plant recombinant humanα-GAL-II from different batches Expected α-GAL Measured α-GAL Batch no.activity [mg/mL] activity [mg/mL] 1 1.25 1.38 2 1.25 1.23 3 1.43 1.4 41.25 0.85 5 1.25 1.11

As shown in Table 9, the measured activity was close to the expectedactivity in all 5 batches. In 4 of the 5 batches, the measured activitydiffered from the expected activity by about 10% or less.

These results indicate that the obtained activity of the cross-linkedprh-α-GAL-II is relatively predictable and reproducible.

The stability of the cross-linked prh-α-GAL-II under lysosomalconditions and in human plasma was determined as described hereinabove.

As shown in FIGS. 40A and 40B, the stability of the cross-linkedprh-α-GAL-II exhibited good reproducibility under both simulatedlysosomal conditions and in human plasma.

The cross-linking was also analyzed by SDS-PAGE analysis, IEF(isoelectric focusing) analysis, and MALDI-TOF mass spectrometry, asdescribed hereinabove. Non-cross-linked prh-α-GAL-II was analyzed forcomparison.

As shown in FIG. 41, the cross-linked prh-α-GAL-II from the differentbatches exhibited the same degree of covalent dimerization underSDS-PAGE analysis.

As shown in FIG. 42, the cross-linked prh-α-GAL-II from the differentbatches exhibited the same isoelectric points under IEF analysis.

As shown in FIGS. 43A-43F, the cross-linked prh-α-GAL-II from batches1-5 (FIGS. 43B-43F, respectively) all exhibited an increase ofapproximately 20-21 KDa in the dimer form, as compared to thenon-cross-linked prh-α-GAL-II (FIG. 43A). Such an increase correspondsto about 10 PEG molecules per α-GAL dimer. As further shown in FIGS.43B-43F, the cross-linked prh-α-GAL-II from the different batchesexhibited similar proportions of monomer vs. dimer.

These results further indicate that good reproducibility incross-linking of α-GAL.

The kinetic parameters of the cross-linked prh-α-GAL-II were determinedusing a pNP-G substrate and Michaelis-Menten analysis, in order toexamine the reproducibility of enzymatic activity. The measurements wereperformed in a solution of 20 mM citrate, 30 mM sodium phosphate, 0.1%bovine serum albumin and 0.67% ethanol, at a pH of 4.6. The kineticparameters were calculated using protein content values based on opticaldensity at 280 nm.

As shown in FIG. 44, the cross-linked prh-α-GAL-II from the differentbatches exhibited similar profiles of catalytic velocity vs. substrateconcentration.

As shown in Table 10 below, the cross-linked prh-α-GAL-II from thedifferent batches exhibited good reproducibility of the V_(max) andk_(cat) parameters. The K_(m) parameter varied more between batches,although this may be an artifact of the protein quantification.

The above results indicate good reproducibility in the enzymaticproperties of cross-linked α-GAL.

TABLE 10 Michaelis-Menten parameters of plant recombinant human α-GAL IIcross-linked with bis-NHS-PEG₄₅ in different batches K_(m) V_(max)k_(cat) k_(cat)/K_(m) Batch no. (μM) (μM/min) (sec⁻¹) (sec⁻¹ μM⁻¹) 14939 3.87 61.92 0.0125 2 2215 3.30 52.86 0.0239 3 4470 3.95 63.12 0.01414 3285 3.72 59.53 0.018 5 2243 3.91 62.60 0.028

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting.

What is claimed is:
 1. A multimeric protein structure comprising twoα-galactosidase monomers, the protein structure being a dimeric proteinstructure, said two α-galactosidase monomers being covalently linked toone another via a linking moiety, and said α-galactosidase comprising anamino acid sequence having at least 95% sequence identity to SEQ ID NO:15, wherein said at least one linking moiety has a general formula:—X₁—(CR₁R₂—CR₃R₄—Y)n-X₂— wherein each of X₁ and X₂ is a functional groupthat forms a covalent bond with at least one α-galactosidase monomer; Cis a carbon atom; Y is an oxygen atom, a sulfur atom or NR₅, wherein NR₅is a nitrogen atom attached to R₅; n is an integer from 5 to 150; andeach of R₁, R₂, R₃, R₄ and R₅ is independently selected from the groupconsisting of hydrogen, alkyl, cycloalkyl, alkenyl, alkynyl, alkoxy,hydroxy, oxo, thiol and thioalkoxy.
 2. The multimeric protein structureof claim 1, wherein at least one of said functional groups forms anamide bond with an α-galactosidase monomer.
 3. The multimeric proteinstructure of claim 1, wherein said linking moiety is at least 20 atomslong.
 4. The multimeric protein structure of claim 1, wherein n is atleast
 25. 5. The multimeric protein structure of claim 1, wherein n isan integer from 40 to
 70. 6. The multimeric protein structure of claim1, wherein each of R₁, R₂, R₃, R₄ and R₅ is independently selected fromthe group consisting of hydrogen and oxo.
 7. The multimeric proteinstructure of claim 1, featuring a characteristic selected from the groupconsisting of: (a) an α-galactosidase activity, upon subjecting themultimeric protein structure to human plasma conditions for one hour,which is at least 10% higher than an activity of native α-galactosidaseupon subjecting said native α-galactosidase to said human plasmaconditions for one hour; (b) an α-galactosidase activity which decreasesupon subjecting the multimeric protein structure to human plasmaconditions for one hour by a percentage which is at least 10% less thanthe percentage by which an activity of said native α-galactosidasedecreases upon subjecting said native α-galactosidase to said humanplasma conditions for one hour; (c) an α-galactosidase activity whichremains in a range of 50% to 150% of the initial activity uponsubjecting the multimeric protein structure to human plasma conditionsfor one hour; (d) an α-galactosidase activity, upon subjecting themultimeric protein structure to lysosomal conditions for one week, whichis at least 10% higher than an activity of native α-galactosidase uponsubjecting said native α-galactosidase to said lysosomal conditions forone week; (e) an α-galactosidase activity which decreases uponsubjecting the multimeric protein structure to lysosomal conditions forone day by a percentage which is at least 10% less than the percentageby which an activity of said native α-galactosidase decreases uponsubjecting said native α-galactosidase to said lysosomal conditions forone day; (f) an α-galactosidase activity which remains in a range of 50%to 150% of the initial activity upon subjecting the multimeric proteinstructure to lysosomal conditions for one day; (g) an α-galactosidaseactivity, immediately upon subjecting the multimeric protein structureto lysosomal conditions, which is at least 10% higher than an activityof native α-galactosidase immediately upon subjecting said nativeα-galactosidase to said lysosomal conditions; (h) an α-galactosidaseactivity, immediately upon subjecting the multimeric protein structureto an aqueous solution having a pH of 7 and a temperature of 37° C.,which is at least 10% higher than an activity of native α-galactosidaseimmediately upon subjecting said native α-galactosidase to said aqueoussolution having a pH of 7 and a temperature of 37° C.; and (i) acirculating half-life in human plasma which is higher than a circulatinghalf-life of said native α-galactosidase.
 8. The multimeric proteinstructure of claim 7, wherein said α-galactosidase activity of saidmultimeric protein structure which remains in a range of 50% to 150% ofthe initial activity upon subjecting the multimeric protein structure tolysosomal conditions for one day, further remains in a range of 50% to150% of the initial activity upon subjecting the multimeric proteinstructure to lysosomal conditions for one week.
 9. The multimericprotein structure of claim 7, wherein said circulating half-life of themultimeric protein structure which is higher than a circulatinghalf-life of said native α-galactosidase, is higher by at least 20% thansaid circulating half-life of said native α-galactosidase.
 10. Themultimeric protein structure of claim 1, characterized by anα-galactosidase activity in an organ upon administration of saidmultimeric protein structure to a vertebrate, said organ being selectedfrom the group consisting of a spleen, a heart and a kidney.
 11. Themultimeric protein structure of claim 1, wherein said α-galactosidase isa human α-galactosidase selected from the group consisting of agalsidasealpha and agalsidase beta.
 12. The multimeric protein structure of claim1, wherein said α-galactosidase is a recombinant α-galactosidase. 13.The multimeric protein structure of claim 1, wherein saidα-galactosidase is a plant recombinant α-galactosidase.
 14. Themultimeric protein structure of claim 1, wherein said α-galactosidasecomprises an amino acid sequence having at least 99% sequence identityto SEQ ID NO:
 15. 15. The multimeric protein structure of claim 1,wherein said α-galactosidase has an amino acid sequence selected fromthe group consisting of SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:3 and SEQ IDNO:
 15. 16. A pharmaceutical composition comprising the multimericprotein structure of claim 1 and a pharmaceutically acceptable carrier.17. The composition of claim 16, wherein said pharmaceuticallyacceptable carrier is an aqueous solution comprising saline and aphysiologically compatible buffer, and said multimeric protein structureis water-soluble.
 18. A method of treating Fabry disease, the methodcomprising administering to a subject in need thereof a therapeuticallyeffective amount of the multimeric protein structure of claim 1, therebytreating the Fabry disease.
 19. A process of preparing the multimericprotein structure of claim 1, the process comprising reactingα-galactosidase with a cross-linking agent which comprises said linkingmoiety and at least two reactive groups.
 20. The process of claim 19,wherein a molar ratio of said cross-linking agent to monomers of saidα-galactosidase is in a range of from 75:1 to 300:1.